Methods and Apparatuses for Providing a Holographic Waveguide Display Using Integrated Gratings

ABSTRACT

Systems and methods for providing holographic waveguide display using integrated gratings in accordance with various embodiments of the invention are illustrated. One embodiment includes a waveguide display including a source of light, and a first waveguide including a grating structure including first and second gratings, and an input coupler configured to couple a first field-of-view portion of light, and couple a second field-of-view portion of light, wherein the first grating is configured to provide beam expansion in a first direction for the first field-of-view portion of light, and provide beam expansion in the first direction and beam extraction towards a viewer for the second field-of-view portion of light, the second grating is configured to provide beam expansion in a second direction for the second field-of-view portion of light, and provide beam expansion in the second direction and beam extraction towards a viewer for the first field-of-view portion of light.

CROSS-REFERENCE TO RELATED APPLICATIONS

The current application is a continuation of U.S. application Ser. No.16/794,071 entitled “Methods and Apparatuses for Providing a HolographicWaveguide Display Using Integrated Gratings,” filed Feb. 18, 2020, whichclaims the benefit of and priority under 35 U.S.C. § 119(e) to U.S.Provisional Patent Application No. 62/806,665 entitled “Methods andApparatuses for Providing a Color Holographic Waveguide Display UsingOverlapping Bragg Gratings,” filed Feb. 15, 2019 and U.S. ProvisionalPatent Application No. 62/813,373 entitled “Improvements to Methods andApparatuses for Providing a Color Holographic Waveguide Display UsingOverlapping Bragg Gratings,” filed Mar. 4, 2019, the disclosures ofwhich are incorporated herein by reference in their entireties.

FIELD OF THE INVENTION

The present invention generally relates to waveguide devices and, morespecifically, to holographic waveguide displays.

BACKGROUND

Waveguides can be referred to as structures with the capability ofconfining and guiding waves (i.e., restricting the spatial region inwhich waves can propagate). One subclass includes optical waveguides,which are structures that can guide electromagnetic waves, typicallythose in the visible spectrum. Waveguide structures can be designed tocontrol the propagation path of waves using a number of differentmechanisms. For example, planar waveguides can be designed to utilizediffraction gratings to diffract and couple incident light into thewaveguide structure such that the in-coupled light can proceed to travelwithin the planar structure via total internal reflection (TIR).

Fabrication of waveguides can include the use of material systems thatallow for the recording of holographic optical elements within thewaveguides. One class of such material includes polymer dispersed liquidcrystal (PDLC) mixtures, which are mixtures containingphotopolymerizable monomers and liquid crystals. A further subclass ofsuch mixtures includes holographic polymer dispersed liquid crystal(HPDLC) mixtures. Holographic optical elements, such as volume phasegratings, can be recorded in such a liquid mixture by illuminating thematerial with two mutually coherent laser beams. During the recordingprocess, the monomers polymerize, and the mixture undergoes aphotopolymerization-induced phase separation, creating regions denselypopulated by liquid crystal micro-droplets, interspersed with regions ofclear polymer. The alternating liquid crystal-rich and liquidcrystal-depleted regions form the fringe planes of the grating. Theresulting grating, which is commonly referred to as a switchable Bragggrating (SBG), has all the properties normally associated with volume orBragg gratings but with much higher refractive index modulation rangescombined with the ability to electrically tune the grating over acontinuous range of diffraction efficiency (the proportion of incidentlight diffracted into a desired direction). The latter can extend fromnon-diffracting (cleared) to diffracting with close to 100% efficiency.

Waveguide optics, such as those described above, can be considered for arange of display and sensor applications. In many applications,waveguides containing one or more grating layers encoding multipleoptical functions can be realized using various waveguide architecturesand material systems, enabling new innovations in near-eye displays foraugmented reality (AR) and virtual reality (VR), compact head-updisplays (HUDs) and helmet-mounted displays or head-mounted displays(HMDs) for road transport, aviation, and military applications, andsensors for biometric and laser radar (LIDAR) applications.

SUMMARY OF THE INVENTION

Systems and methods for providing holographic waveguide display usingintegrated gratings in accordance with various embodiments of theinvention are illustrated. One embodiment includes a waveguide displayincluding a source of light, and a first waveguide including a gratingstructure including first and second gratings, and an input couplerconfigured to couple a first field-of-view portion of light from thesource of light into the first waveguide and towards the first grating,and couple a second field-of-view portion of light from the source oflight into the first waveguide and towards the second grating, whereinthe first grating is configured to provide beam expansion in a firstdirection for the first field-of-view portion of light, and provide beamexpansion in the first direction and beam extraction towards a viewerfor the second field-of-view portion of light, the second grating isconfigured to provide beam expansion in a second direction for thesecond field-of-view portion of light, and provide beam expansion in thesecond direction and beam extraction towards a viewer for the firstfield-of-view portion of light, the input coupler, the first grating,and the second grating each includes a grating vector, and the gratingvectors of the input coupler, the first grating, and the second gratingprovide a resultant vector with substantially zero magnitude.

In another embodiment, the first grating includes first and secondgrating prescriptions, and the second grating includes third and fourthgrating prescriptions, wherein the first grating prescription isconfigured to provide the beam expansion in the first direction for thefirst field-of-view portion of light, the second grating prescription isconfigured to provide beam expansion in the first direction and beamextraction towards a viewer for the second field-of-view portion oflight, the third grating prescription is configured to provide the beamexpansion in the second direction for the second field-of-view portionof light, and the fourth grating prescription is configured to providethe beam expansion in the second direction and beam extraction towards aviewer for the first field-of-view portion of light.

In a further embodiment, the first and second grating prescriptions areat least partially multiplexed, and the third and fourth gratingprescriptions are at least partially multiplexed.

In still another embodiment, the first grating at least partiallyoverlaps the second grating.

In a still further embodiment, the first waveguide includes first andsecond grating layers, the first grating is disposed within the firstgrating layer, and the second grating is disposed within the secondgrating layer.

In yet another embodiment, the first waveguide further includes atransparent layer disposed between and adjacent the first and secondgrating layers.

In a yet further embodiment, the waveguide display further includes asecond waveguide, wherein the first waveguide is configured to couple ina first spectral band of light, and the second waveguide is configuredto couple in a second spectral band of light.

In another additional embodiment, wherein the input coupler includes aninput configuration selected from at least one of an input prism, aninput grating, first and second input gratings, and an input gratingincluding two multiplexed grating prescriptions.

In a further additional embodiment, the grating vector of the inputcoupler has a different magnitude than the grating vector of the firstgrating.

In another embodiment again, the source of light provides at least twodifferent wavelengths of light.

In a further embodiment again, a method of displaying an image, themethod including providing a waveguide display including a firstwaveguide supporting an input coupler and a grating structure includingfirst and second gratings, wherein the input coupler, the first grating,and the second grating each includes a grating vector, wherein thegrating vectors of the input coupler, the first grating, and the secondgrating provide a resultant vector with substantially zero magnitude,coupling a first field of view portion into the waveguide via the inputcoupler, coupling a second field-of-view portion into the waveguide viathe input coupler, expanding the first field-of-view portion light in afirst direction using the first grating, expanding the firstfield-of-view portion light in a second direction and extracting it fromthe waveguide using the second grating, expanding the secondfield-of-view portion light in the second direction using the secondgrating, and expanding the second field of view portion light in thefirst direction and extracting it from the waveguide using the firstgrating.

In still yet another embodiment, the first grating includes first andsecond grating prescriptions, and the second grating includes third andfourth grating prescriptions, wherein the first field-of-view portionlight is expanded in the first direction using the first gratingprescription, the second field-of-view portion light is expanded in thefirst direction and extracted from the waveguide using the secondgrating prescription, the second field-of-view portion light is expandedin the second direction using the third grating prescription, and thefirst field-of-view portion light is expanded in the second directionand extracted from the waveguide using the fourth grating prescription.

In a still yet further embodiment, the first and second gratingprescriptions are at least partially multiplexed, and the third andfourth grating prescriptions are at least partially multiplexed.

In still another additional embodiment, the first grating at leastpartially overlaps the second grating.

In a still further additional embodiment, the first waveguide includesfirst and second grating layers, the first grating is disposed withinthe first grating layer, and the second grating is disposed within thesecond grating layer.

In still another embodiment again, the first waveguide further includesa transparent layer disposed between and adjacent the first and secondgrating layers.

In a still further embodiment again, the waveguide display furtherincludes a second waveguide, wherein the first waveguide is configuredto couple in a first spectral band of light, and the second waveguide isconfigured to couple in a second spectral band of light.

In yet another additional embodiment, the input coupler includes aninput configuration selected from at least one of an input prism, aninput grating, first and second input gratings, and an input gratingcomprising two multiplexed grating prescriptions.

In a yet further additional embodiment, the grating vector of the inputcoupler has a different magnitude than the grating vector of the firstgrating.

In yet another embodiment again, the source of light provides at leasttwo different wavelengths of light.

Additional embodiments and features are set forth in part in thedescription that follows, and in part will become apparent to thoseskilled in the art upon examination of the specification or may belearned by the practice of the invention. A further understanding of thenature and advantages of the present invention may be realized byreference to the remaining portions of the specification and thedrawings, which forms a part of this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The description will be more fully understood with reference to thefollowing figures and data graphs, which are presented as exemplaryembodiments of the invention and should not be construed as a completerecitation of the scope of the invention.

FIG. 1 conceptually illustrates a waveguide display in accordance withan embodiment of the invention.

FIG. 2 conceptually illustrates a color waveguide display having twoblue-green diffracting waveguides and two green-red diffractingwaveguides in accordance with an embodiment of the invention.

FIGS. 3A-3C conceptually illustrate integrated gratings in accordancewith various embodiments of the invention.

FIGS. 4A-4C schematically illustrate ray propagation through a gratingstructure having an input grating and two integrated gratings inaccordance with an embodiment of the invention.

FIGS. 5A-5E conceptually illustrate various grating vectorconfigurations in accordance with various embodiments of the invention.

FIG. 6 conceptually illustrates a schematic plan view of a gratingarchitecture having an input grating and integrated gratings inaccordance with an embodiment of the invention.

FIG. 7 shows a flow diagram conceptually illustrating a method ofdisplaying an image in accordance with an embodiment of the invention.

FIG. 8 shows a flow diagram conceptually illustrating a method ofdisplaying an image utilizing integrated gratings containing multiplegratings in accordance with an embodiment of the invention.

FIG. 9 conceptually illustrates a profile view of two overlappingwaveguide portions implementing integrated gratings in accordance withan embodiment of the invention.

FIG. 10 conceptually illustrates a schematic plan view of a gratingarchitecture having two sets of integrated gratings in accordance withan embodiment of the invention.

FIG. 11 conceptually illustrates a plot of diffraction efficiency versusangle for a waveguide for diffractions occurring at differentfield-of-view angles in accordance with an embodiment of the invention.

FIG. 12 shows the viewing geometry provided by a waveguide in accordancewith an embodiment of the invention.

FIG. 13 conceptually illustrates the field-of-view geometry for abinocular display with binocular overlap between the left and right eyeimages provided by a waveguide in accordance with an embodiment of theinvention.

DETAILED DESCRIPTION

For the purposes of describing embodiments, some well-known features ofoptical technology known to those skilled in the art of optical designand visual displays have been omitted or simplified in order to notobscure the basic principles of the invention. Unless otherwise stated,the term “on-axis” in relation to a ray or a beam direction refers topropagation parallel to an axis normal to the surfaces of the opticalcomponents described in relation to the invention. In the followingdescription the terms light, ray, beam, and direction may be usedinterchangeably and in association with each other to indicate thedirection of propagation of electromagnetic radiation along rectilineartrajectories. The term light and illumination may be used in relation tothe visible and infrared bands of the electromagnetic spectrum. Parts ofthe following description will be presented using terminology commonlyemployed by those skilled in the art of optical design. As used herein,the term grating may encompass a grating comprised of a set of gratingsin some embodiments. For illustrative purposes, it is to be understoodthat the drawings are not drawn to scale unless stated otherwise.

Waveguide displays in accordance with various embodiments of theinvention can be implemented using many different techniques. Waveguidetechnology can enable low cost, efficient, and versatile diffractiveoptical solutions for many different applications. One commonly usedwaveguide architecture includes an input grating for coupling light froman image source into a TIR path in the waveguide, a fold grating forproviding beam expansion in a first direction, and an output grating forproviding a second beam expansion in a direction orthogonal to the firstdirection and extracting the pupil-expanded beam from the waveguide forviewing from an exit pupil or eyebox. While effective at two-dimensionalbeam expansion and extraction, this arrangement typically demands alarge grating area. When used with birefringent gratings, thisarchitecture can also suffer from haze that arises from millions ofgrating interactions in the fold. A further issue is image nonuniformitydue to longer light paths incurring more beam interactions with thesubstrates of the waveguide. As such, many embodiments of the inventionare directed towards wide angle, low cost, efficient, and compactwaveguide displays.

In many embodiments, the waveguide display includes at least one inputgrating and at least two integrated gratings, each capable of performingthe functions of traditional fold and output gratings. In furtherembodiments, a single multiplexed input grating is implemented toprovide input light with two bifurcated paths. In other embodiments, twoinput gratings are implemented to provide bifurcated optical paths. Inaddition to the different configurations of the input grating(s), theintegrated gratings can also be configured in various ways. In someembodiments, the integrated gratings contain crossed grating vectors andcan be configured to provide beam expansion in two directions and beamextraction for light coming from the input grating(s). In severalembodiments, the integrated gratings are configured as overlappinggratings with crossed grating vectors. The integrated nature of thegrating architecture can allow for a compact waveguide display that issuitable for various applications, including but not limited to AR, VR,HUD, and LIDAR applications. As can readily be appreciated, the specificarchitecture and implementation of the waveguide display can depend onthe specific requirements of a given application. For example, in someembodiments, the waveguide display is implemented with integratedgratings to provide a binocular field-of-view of at least 50° diagonal.In further embodiments, the waveguide display is implemented withintegrated gratings to provide a binocular field-of-view of at least˜100° diagonal. Waveguide displays, grating architecture, HPDLCmaterials, and manufacturing processes in accordance with variousembodiments of the invention are discussed below in further detail.

Optical Waveguide and Grating Structures

Optical structures recorded in waveguides can include many differenttypes of optical elements, such as but not limited to diffractiongratings. Gratings can be implemented to perform various opticalfunctions, including but not limited to coupling light, directing light,and preventing the transmission of light. In many embodiments, thegratings are surface relief gratings that reside on the outer surface ofthe waveguide. In other embodiments, the grating implemented is a Bragggrating (also referred to as a volume grating), which are structureshaving a periodic refractive index modulation. Bragg gratings can befabricated using a variety of different methods. One process includesinterferential exposure of holographic photopolymer materials to formperiodic structures. Bragg gratings can have high efficiency with littlelight being diffracted into higher orders. The relative amount of lightin the diffracted and zero order can be varied by controlling therefractive index modulation of the grating, a property that can be usedto make lossy waveguide gratings for extracting light over a largepupil.

One class of Bragg gratings used in holographic waveguide devices is theSwitchable Bragg Grating (SBG). SBGs can be fabricated by first placinga thin film of a mixture of photopolymerizable monomers and liquidcrystal material between substrates. The substrates can be made ofvarious types of materials, such glass and plastics. In many cases, thesubstrates are in a parallel configuration. In other embodiments, thesubstrates form a wedge shape. One or both substrates can supportelectrodes, typically transparent tin oxide films, for applying anelectric field across the film. The grating structure in an SBG can berecorded in the liquid material (often referred to as the syrup) throughphotopolymerization-induced phase separation using interferentialexposure with a spatially periodic intensity modulation. Factors such asbut not limited to control of the irradiation intensity, componentvolume fractions of the materials in the mixture, and exposuretemperature can determine the resulting grating morphology andperformance. As can readily be appreciated, a wide variety of materialsand mixtures can be used depending on the specific requirements of agiven application. In many embodiments, HPDLC material is used. Duringthe recording process, the monomers polymerize, and the mixtureundergoes a phase separation. The LC molecules aggregate to formdiscrete or coalesced droplets that are periodically distributed inpolymer networks on the scale of optical wavelengths. The alternatingliquid crystal-rich and liquid crystal-depleted regions form the fringeplanes of the grating, which can produce Bragg diffraction with a strongoptical polarization resulting from the orientation ordering of the LCmolecules in the droplets.

The resulting volume phase grating can exhibit very high diffractionefficiency, which can be controlled by the magnitude of the electricfield applied across the film. When an electric field is applied to thegrating via transparent electrodes, the natural orientation of the LCdroplets can change, causing the refractive index modulation of thefringes to lower and the hologram diffraction efficiency to drop to verylow levels. Typically, the electrodes are configured such that theapplied electric field will be perpendicular to the substrates. In anumber of embodiments, the electrodes are fabricated from indium tinoxide (ITO). In the OFF state with no electric field applied, theextraordinary axis of the liquid crystals generally aligns normal to thefringes. The grating thus exhibits high refractive index modulation andhigh diffraction efficiency for P-polarized light. When an electricfield is applied to the HPDLC, the grating switches to the ON statewherein the extraordinary axes of the liquid crystal molecules alignparallel to the applied field and hence perpendicular to the substrate.In the ON state, the grating exhibits lower refractive index modulationand lower diffraction efficiency for both S- and P-polarized light.Thus, the grating region no longer diffracts light. Each grating regioncan be divided into a multiplicity of grating elements such as forexample a pixel matrix according to the function of the HPDLC device.Typically, the electrode on one substrate surface is uniform andcontinuous, while electrodes on the opposing substrate surface arepatterned in accordance to the multiplicity of selectively switchablegrating elements.

Typically, the SBG elements are switched clear in 30 μs with a longerrelaxation time to switch ON. The diffraction efficiency of the devicecan be adjusted, by means of the applied voltage, over a continuousrange. In many cases, the device exhibits near 100% efficiency with novoltage applied and essentially zero efficiency with a sufficiently highvoltage applied. In certain types of HPDLC devices, magnetic fields canbe used to control the LC orientation. In some HPDLC applications, phaseseparation of the LC material from the polymer can be accomplished tosuch a degree that no discernible droplet structure results. An SBG canalso be used as a passive grating. In this mode, its chief benefit is auniquely high refractive index modulation. SBGs can be used to providetransmission or reflection gratings for free space applications. SBGscan be implemented as waveguide devices in which the HPDLC forms eitherthe waveguide core or an evanescently coupled layer in proximity to thewaveguide. The substrates used to form the HPDLC cell provide a totalinternal reflection (TIR) light guiding structure. Light can be coupledout of the SBG when the switchable grating diffracts the light at anangle beyond the TIR condition.

In some embodiments, LC can be extracted or evacuated from the SBG toprovide a surface relief grating (SRG) that has properties very similarto a Bragg grating due to the depth of the SRG structure (which is muchgreater than that practically achievable using surface etching and otherconventional processes commonly used to fabricate SRGs). The LC can beextracted using a variety of different methods, including but notlimited to flushing with isopropyl alcohol and solvents. In manyembodiments, one of the transparent substrates of the SBG is removed,and the LC is extracted. In further embodiments, the removed substrateis replaced. The SRG can be at least partially backfilled with amaterial of higher or lower refractive index. Such gratings offer scopefor tailoring the efficiency, angular/spectral response, polarization,and other properties to suit various waveguide applications.

Waveguides in accordance with various embodiments of the invention caninclude various grating configurations designed for specific purposesand functions. In many embodiments, the waveguide is designed toimplement a grating configuration capable of preserving eyebox sizewhile reducing lens size by effectively expanding the exit pupil of acollimating optical system. The exit pupil can be defined as a virtualaperture where only the light rays which pass though this virtualaperture can enter the eyes of a user. In some embodiments, thewaveguide includes an input grating optically coupled to a light source,a fold grating for providing a first direction beam expansion, and anoutput grating for providing beam expansion in a second direction, whichis typically orthogonal to the first direction, and beam extractiontowards the eyebox. As can readily be appreciated, the gratingconfiguration implemented waveguide architectures can depend on thespecific requirements of a given application. In some embodiments, thegrating configuration includes multiple fold gratings. In severalembodiments, the grating configuration includes an input grating and asecond grating for performing beam expansion and beam extractionsimultaneously. The second grating can include gratings of differentprescriptions, for propagating different portions of the field-of-view,arranged in separate overlapping grating layers or multiplexed in asingle grating layer. Furthermore, various types of gratings andwaveguide architectures can also be utilized.

In several embodiments, the gratings within each layer are designed tohave different spectral and/or angular responses. For example, in manyembodiments, different gratings across different grating layers areoverlapped, or multiplexed, to provide an increase in spectralbandwidth. In some embodiments, a full color waveguide is implementedusing three grating layers, each designed to operate in a differentspectral band (red, green, and blue). In other embodiments, a full colorwaveguide is implemented using two grating layers, a red-green gratinglayer and a green-blue grating layer. As can readily be appreciated,such techniques can be implemented similarly for increasing angularbandwidth operation of the waveguide. In addition to the multiplexing ofgratings across different grating layers, multiple gratings can bemultiplexed within a single grating layer—i.e., multiple gratings can besuperimposed within the same volume. In several embodiments, thewaveguide includes at least one grating layer having two or more gratingprescriptions multiplexed in the same volume. In further embodiments,the waveguide includes two grating layers, each layer having two gratingprescriptions multiplexed in the same volume. Multiplexing two or moregrating prescriptions within the same volume can be achieved usingvarious fabrication techniques. In a number of embodiments, amultiplexed master grating is utilized with an exposure configuration toform a multiplexed grating. In many embodiments, a multiplexed gratingis fabricated by sequentially exposing an optical recording materiallayer with two or more configurations of exposure light, where eachconfiguration is designed to form a grating prescription. In someembodiments, a multiplexed grating is fabricated by exposing an opticalrecording material layer by alternating between or among two or moreconfigurations of exposure light, where each configuration is designedto form a grating prescription. As can readily be appreciated, varioustechniques, including those well known in the art, can be used asappropriate to fabricate multiplexed gratings.

In many embodiments, the waveguide can incorporate at least one of:angle multiplexed gratings, color multiplexed gratings, fold gratings,dual interaction gratings, rolled K-vector gratings, crossed foldgratings, tessellated gratings, chirped gratings, gratings withspatially varying refractive index modulation, gratings having spatiallyvarying grating thickness, gratings having spatially varying averagerefractive index, gratings with spatially varying refractive indexmodulation tensors, and gratings having spatially varying averagerefractive index tensors. In some embodiments, the waveguide canincorporate at least one of: a half wave plate, a quarter wave plate, ananti-reflection coating, a beam splitting layer, an alignment layer, aphotochromic back layer for glare reduction, and louvre films for glarereduction. In several embodiments, the waveguide can support gratingsproviding separate optical paths for different polarizations. In variousembodiments, the waveguide can support gratings providing separateoptical paths for different spectral bandwidths. In a number ofembodiments, the gratings can be HPDLC gratings, switching gratingsrecorded in HPDLC (such switchable Bragg Gratings), Bragg gratingsrecorded in holographic photopolymer, or surface relief gratings. Inmany embodiments, the waveguide operates in a monochrome band. In someembodiments, the waveguide operates in the green band. In severalembodiments, waveguide layers operating in different spectral bands suchas red, green, and blue (RGB) can be stacked to provide a three-layerwaveguiding structure. In further embodiments, the layers are stackedwith air gaps between the waveguide layers. In various embodiments, thewaveguide layers operate in broader bands such as blue-green andgreen-red to provide two-waveguide layer solutions. In otherembodiments, the gratings are color multiplexed to reduce the number ofgrating layers. Various types of gratings can be implemented. In someembodiments, at least one grating in each layer is a switchable grating.

Waveguides incorporating optical structures such as those discussedabove can be implemented in a variety of different applications,including but not limited to waveguide displays. In various embodiments,the waveguide display is implemented with an eyebox of greater than 10mm with an eye relief greater than 25 mm. In some embodiments, thewaveguide display includes a waveguide with a thickness between 2.0-5.0mm. In many embodiments, the waveguide display can provide an imagefield-of-view of at least 50° diagonal. In further embodiments, thewaveguide display can provide an image field-of-view of at least 70°diagonal. The waveguide display can employ many different types ofpicture generation units (PGUs). In several embodiments, the PGU can bea reflective or transmissive spatial light modulator such as a liquidcrystal on Silicon (LCoS) panel or a micro electromechanical system(MEMS) panel. In a number of embodiments, the PGU can be an emissivedevice such as an organic light emitting diode (OLED) panel. In someembodiments, an OLED display can have a luminance greater than 4000 nitsand a resolution of 4kx4k pixels. In several embodiments, the waveguidecan have an optical efficiency greater than 10% such that a greater than400 nit image luminance can be provided using an OLED display ofluminance 4000 nits. Waveguides implementing P-diffracting gratings(i.e., gratings with high efficiency for P-polarized light) typicallyhave a waveguide efficiency of 5%-6.2%. Since P-diffracting orS-diffracting gratings can waste half of the light from an unpolarizedsource such as an OLED panel, many embodiments are directed towardswaveguides capable of providing both S-diffracting and P-diffractinggratings to allow for an increase in the efficiency of the waveguide byup to a factor of two. In some embodiments, the S-diffracting andP-diffracting gratings are implemented in separate overlapping gratinglayers. Alternatively, a single grating can, under certain conditions,provide high efficiency for both p-polarized and s-polarized light. Inseveral embodiments, the waveguide includes Bragg-like gratings producedby extracting LC from HPDLC gratings, such as those described above, toenable high S and P diffraction efficiency over certain wavelength andangle ranges for suitably chosen values of grating thickness (typically,in the range 2-5 μm).

Optical Recording Material Systems

HPDLC mixtures generally include LC, monomers, photoinitiator dyes, andcoinitiators. The mixture (often referred to as syrup) frequently alsoincludes a surfactant. For the purposes of describing the invention, asurfactant is defined as any chemical agent that lowers the surfacetension of the total liquid mixture. The use of surfactants in PDLCmixtures is known and dates back to the earliest investigations ofPDLCs. For example, a paper by R. L Sutherland et al., SPIE Vol. 2689,158-169, 1996, the disclosure of which is incorporated herein byreference, describes a PDLC mixture including a monomer, photoinitiator,coinitiator, chain extender, and LCs to which a surfactant can be added.Surfactants are also mentioned in a paper by Natarajan et al, Journal ofNonlinear Optical Physics and Materials, Vol. 5 No. I 89-98, 1996, thedisclosure of which is incorporated herein by reference. Furthermore,U.S. Pat. No. 7,018,563 by Sutherland; et al., discussespolymer-dispersed liquid crystal material for forming apolymer-dispersed liquid crystal optical element having: at least oneacrylic acid monomer; at least one type of liquid crystal material; aphotoinitiator dye; a coinitiator; and a surfactant. The disclosure ofU.S. Pat. No. 7,018,563 is hereby incorporated by reference in itsentirety.

The patent and scientific literature contains many examples of materialsystems and processes that can be used to fabricate SBGs, includinginvestigations into formulating such material systems for achieving highdiffraction efficiency, fast response time, low drive voltage, and soforth. U.S. Pat. No. 5,942,157 by Sutherland, and U.S. Pat. No.5,751,452 by Tanaka et al. both describe monomer and liquid crystalmaterial combinations suitable for fabricating SBG devices. Examples ofrecipes can also be found in papers dating back to the early 1990s. Manyof these materials use acrylate monomers, including:

-   -   R. L. Sutherland et al., Chem. Mater. 5, 1533 (1993), the        disclosure of which is incorporated herein by reference,        describes the use of acrylate polymers and surfactants.        Specifically, the recipe comprises a crosslinking        multifunctional acrylate monomer; a chain extender N-vinyl        pyrrolidinone, LC E7, photo-initiator rose Bengal, and        coinitiator N-phenyl glycine. Surfactant octanoic acid was added        in certain variants.    -   Fontecchio et al., SID 00 Digest 774-776, 2000, the disclosure        of which is incorporated herein by reference, describes a UV        curable HPDLC for reflective display applications including a        multi-functional acrylate monomer, LC, a photoinitiator, a        coinitiators, and a chain terminator.    -   Y. H. Cho, et al., Polymer International, 48, 1085-1090, 1999,        the disclosure of which is incorporated herein by reference,        discloses HPDLC recipes including acrylates.    -   Karasawa et al., Japanese Journal of Applied Physics, Vol. 36,        6388-6392, 1997, the disclosure of which is incorporated herein        by reference, describes acrylates of various functional orders.    -   T. J. Bunning et al., Polymer Science: Part B: Polymer Physics,        Vol. 35, 2825-2833, 1997, the disclosure of which is        incorporated herein by reference, also describes multifunctional        acrylate monomers.    -   G. S. Iannacchione et al., Europhysics Letters Vol. 36 (6).        425-430, 1996, the disclosure of which is incorporated herein by        reference, describes a PDLC mixture including a penta-acrylate        monomer, LC, chain extender, coinitiators, and photoinitiator.

Acrylates offer the benefits of fast kinetics, good mixing with othermaterials, and compatibility with film forming processes. Sinceacrylates are cross-linked, they tend to be mechanically robust andflexible. For example, urethane acrylates of functionality 2 (di) and 3(tri) have been used extensively for HPDLC technology. Higherfunctionality materials such as penta and hex functional stems have alsobeen used.

Modulation of Material Composition

High luminance and excellent color fidelity are important factors in ARwaveguide displays. In each case, high uniformity across the FOV can bedesired. However, the fundamental optics of waveguides can lead tonon-uniformities due to gaps or overlaps of beams bouncing down thewaveguide. Further non-uniformities may arise from imperfections in thegratings and non-planarity of the waveguide substrates. In SBGs, therecan exist a further issue of polarization rotation by birefringentgratings. In applicable cases, the biggest challenge is usually the foldgrating where there are millions of light paths resulting from multipleintersections of the beam with the grating fringes. Careful managementof grating properties, particularly the refractive index modulation, canbe utilized to overcome non-uniformity.

Out of the multitude of possible beam interactions (diffraction or zeroorder transmission), only a subset contributes to the signal presentedat the eye box. By reverse tracing from the eyebox, fold regionscontributing to a given field point can be pinpointed. The precisecorrection to the modulation that is needed to send more into the darkregions of the output illumination can then be calculated. Havingbrought the output illumination uniformity for one color back on target,the procedure can be repeated for other colors. Once the indexmodulation pattern has been established, the design can be exported tothe deposition mechanism, with each target index modulation translatingto a unique deposition setting for each spatial resolution cell on thesubstrate to be coated/deposited. The resolution of the depositionmechanism can depend on the technical limitations of the systemutilized. In many embodiments, the spatial pattern can be implemented to30 micrometers resolution with full repeatability.

Compared with waveguides utilizing surface relief gratings (SRGs), SBGwaveguides implementing manufacturing techniques in accordance withvarious embodiments of the invention can allow for the grating designparameters that impact efficiency and uniformity, such as but notlimited to refractive index modulation and grating thickness, to beadjusted dynamically during the deposition process without the need fora different master. With SRGs where modulation is controlled by etchdepth, such schemes would not be practical as each variation of thegrating would entail repeating the complex and expensive toolingprocess. Additionally, achieving the required etch depth precision andresist imaging complexity can be very difficult.

Deposition processes in accordance with various embodiments of theinvention can provide for the adjustment of grating design parameters bycontrolling the type of material that is to be deposited. Variousembodiments of the invention can be configured to deposit differentmaterials, or different material compositions, in different areas on thesubstrate. For example, deposition processes can be configured todeposit HPDLC material onto an area of a substrate that is meant to be agrating region and to deposit monomer onto an area of the substrate thatis meant to be a non-grating region. In several embodiments, thedeposition process is configured to deposit a layer of optical recordingmaterial that varies spatially in component composition, allowing forthe modulation of various aspects of the deposited material. Thedeposition of material with different compositions can be implemented inseveral different ways. In many embodiments, more than one depositionhead can be utilized to deposit different materials and mixtures. Eachdeposition head can be coupled to a different material/mixturereservoir. Such implementations can be used for a variety ofapplications. For example, different materials can be deposited forgrating and non-grating areas of a waveguide cell. In some embodiments,HPDLC material is deposited onto the grating regions while only monomeris deposited onto the non-grating regions. In several embodiments, thedeposition mechanism can be configured to deposit mixtures withdifferent component compositions.

In some embodiments, spraying nozzles can be implemented to depositmultiple types of materials onto a single substrate. In waveguideapplications, the spraying nozzles can be used to deposit differentmaterials for grating and non-grating areas of the waveguide. In manyembodiments, the spraying mechanism is configured for printing gratingsin which at least one the material composition, birefringence, and/orthickness can be controlled using a deposition apparatus having at leasttwo selectable spray heads. In some embodiments, the manufacturingsystem provides an apparatus for depositing grating recording materialoptimized for the control of laser banding. In several embodiments, themanufacturing system provides an apparatus for depositing gratingrecording material optimized for the control of polarizationnon-uniformity. In several embodiments, the manufacturing systemprovides an apparatus for depositing grating recording materialoptimized for the control of polarization non-uniformity in associationwith an alignment control layer. In a number of embodiments, thedeposition workcell can be configured for the deposition of additionallayers such as beam splitting coatings and environmental protectionlayers. Inkjet print heads can also be implemented to print differentmaterials in different regions of the substrate.

As discussed above, deposition processes can be configured to depositoptical recording material that varies spatially in componentcomposition. Modulation of material composition can be implemented inmany different ways. In a number of embodiments, an inkjet print headcan be configured to modulate material composition by utilizing thevarious inkjet nozzles within the print head. By altering thecomposition on a “ dot-by-dot” basis, the layer of optical recordingmaterial can be deposited such that it has a varying composition acrossthe planar surface of the layer. Such a system can be implemented usinga variety of apparatuses including but not limited to inkjet printheads. Similar to how color systems use a palette of only a few colorsto produce a spectrum of millions of discrete color values, such as theCMYK system in printers or the additive RGB system in displayapplications, inkjet print heads in accordance with various embodimentsof the invention can be configured to print optical recording materialswith varying compositions using only a few reservoirs of differentmaterials. Different types of inkjet print heads can have differentprecision levels and can print with different resolutions. In manyembodiments, a 300 DPI (“dots per inch”) inkjet print head is utilized.Depending on the precision level, discretization of varying compositionsof a given number of materials can be determined across a given area.For example, given two types of materials to be printed and an inkjetprint head with a precision level of 300 DPI, there are 90,001 possiblediscrete values of composition ratios of the two types of materialsacross a square inch for a given volume of printed material if each dotlocation can contain either one of the two types of materials. In someembodiments, each dot location can contain either one of the two typesof materials or both materials. In several embodiments, more than oneinkjet print head is configured to print a layer of optical recordingmaterial with a spatially varying composition. Although the printing ofdots in a two-material application is essentially a binary system,averaging the printed dots across an area can allow for discretizationof a sliding scale of ratios of the two materials to be printed. Forexample, the amount of discrete levels of possible concentrations/ratiosacross a unit square is given by how many dot locations can be printedwithin the unit square. As such, there can be a range of differentconcentration combinations, ranging from 100% of the first material to100% of the second material. As can readily be appreciated, the conceptsare applicable to real units and can be determined by the precisionlevel of the inkjet print head. Although specific examples of modulatingthe material composition of the printed layer are discussed, the conceptof modulating material composition using inkjet print heads can beexpanded to use more than two different material reservoirs and can varyin precision levels, which largely depends on the types of print headsused.

Varying the composition of the material printed can be advantageous forseveral reasons. For example, in many embodiments, varying thecomposition of the material during deposition can allow for theformation of a waveguide with gratings that have spatially varyingdiffraction efficiencies across different areas of the gratings. Inembodiments utilizing HPDLC mixtures, this can be achieved by modulatingthe relative concentration of liquid crystals in the HPDLC mixtureduring the printing process, which creates compositions that can producegratings with varying diffraction efficiencies when the material isexposed. In several embodiments, a first HPDLC mixture with a certainconcentration of liquid crystals and a second HPDLC mixture that isliquid crystal-free are used as the printing palette in an inkjet printhead for modulating the diffraction efficiencies of gratings that can beformed in the printed material. In such embodiments, discretization canbe determined based on the precision of the inkjet print head. Adiscrete level can be given by the concentration/ratio of the materialsprinted across a certain area. In this example, the discrete levelsrange from no liquid crystal to the maximum concentration of liquidcrystals in the first PDLC mixture.

The ability to vary the diffraction efficiency across a waveguide can beused for various purposes. A waveguide is typically designed to guidelight internally by reflecting the light many times between the twoplanar surfaces of the waveguide. These multiple reflections can allowfor the light path to interact with a grating multiple times. In manyembodiments, a layer of material can be printed with varying compositionof materials such that the gratings formed have spatially varyingdiffraction efficiencies to compensate for the loss of light duringinteractions with the gratings to allow for a uniform output intensity.For example, in some waveguide applications, an output grating isconfigured to provide exit pupil expansion in one direction while alsocoupling light out of the waveguide. The output grating can be designedsuch that when light within the waveguide interact with the grating,only a percentage of the light is refracted out of the waveguide. Theremaining portion continues in the same light path, which remains withinTIR and continues to be reflected within the waveguide. Upon a secondinteraction with the same output grating again, another portion of lightis refracted out of the waveguide. During each refraction, the amount oflight still traveling within the waveguide decreases by the amountrefracted out of the waveguide. As such, the portions refracted at eachinteraction gradually decreases in terms of total intensity. By varyingthe diffraction efficiency of the grating such that it increases withpropagation distance, the decrease in output intensity along eachinteraction can be compensated, allowing for a uniform output intensity.

Varying the diffraction efficiency can also be used to compensate forother attenuation of light within a waveguide. All objects have a degreeof reflection and absorption. Light trapped in TIR within a waveguideare continually reflected between the two surfaces of the waveguide.Depending on the material that makes up the surfaces, portions of lightcan be absorbed by the material during each interaction. In many cases,this attenuation is small, but can be substantial across a large areawhere many reflections occur. In many embodiments, a waveguide cell canbe printed with varying compositions such that the gratings formed fromthe optical recording material layer have varying diffractionefficiencies to compensate for the absorption of light from thesubstrates. Depending on the substrates, certain wavelengths can be moreprone to absorption by the substrates. In a multi-layered waveguidedesign, each layer can be designed to couple in a certain range ofwavelengths of light. Accordingly, the light coupled by these individuallayers can be absorbed in different amounts by the substrates of thelayers. For example, in a number of embodiments, the waveguide is madeof a three-layered stack to implement a full color display, where eachlayer is designed for one of red, green, and blue. In such embodiments,gratings within each of the waveguide layers can be formed to havevarying diffraction efficiencies to perform color balance optimizationby compensating for color imbalance due to loss of transmission ofcertain wavelengths of light.

In addition to varying the liquid crystal concentration within thematerial in order to vary the diffraction efficiency, another techniqueincludes varying the thickness of the waveguide cell. This can beaccomplished through the use of spacers. In many embodiments, spacersare dispersed throughout the optical recording material for structuralsupport during the construction of the waveguide cell. In someembodiments, different sizes of spacers are dispersed throughout theoptical recording material. The spacers can be dispersed in ascendingorder of sizes across one direction of the layer of optical recordingmaterial. When the waveguide cell is constructed through lamination, thesubstrates sandwich the optical recording material and, with structuralsupport from the varying sizes of spacers, create a wedge-shaped layerof optical recording material. spacers of varying sizes can be dispersedsimilar to the modulation process described above. Additionally,modulating spacer sizes can be combined with modulation of materialcompositions. In several embodiments, reservoirs of HPDLC materials eachsuspended with spacers of different sizes are used to print a layer ofHPDLC material with spacers of varying sizes strategically dispersed toform a wedge-shaped waveguide cell. In a number of embodiments, spacersize modulation is combined with material composition modulation byproviding a number of reservoirs equal to the product of the number ofdifferent sizes of spacers and the number of different materials used.For example, in one embodiment, the inkjet print head is configured toprint varying concentrations of liquid crystal with two different spacersizes. In such an embodiment, four reservoirs can be prepared: a liquidcrystal-free mixture suspension with spacers of a first size, a liquidcrystal-free mixture-suspension with spacers of a second size, a liquidcrystal-rich mixture-suspension with spacers of a first size, and aliquid crystal-rich mixture-suspension with spacers of a second size.Further discussion regarding material modulation can be found in U.S.application Ser. No. 16/203,071 filed Nov. 18, 2018 entitled “SYSTEMSAND METHODS FOR MANUFACTURING WAVEGUIDE CELLS.” The disclosure of U.S.application Ser. No. 16/203,491 is hereby incorporated by reference inits entirety for all purposes.

Multi-Layered Waveguide Fabrication

Waveguide manufacturing in accordance with various embodiments of theinvention can be implemented for the fabrication of multi-layeredwaveguides. Multi-layered waveguides refer to a class of waveguides thatutilizes two or more layers having gratings or other optical structures.Although the discussions below may pertain to gratings, any type ofholographic optical structure can be implemented and substituted asappropriate. Multi-layered waveguides can be implemented for variouspurposes, including but not limited to improving spectral and/or angularbandwidths. Traditionally, multi-layered waveguides are formed bystacking and aligning waveguides having a single grating layer. In suchcases, each grating layer is typically bounded by a pair of transparentsubstrates. To maintain the desired total internal reflectioncharacteristics, the waveguides are usually stacked using spacers toform air gaps between the individual waveguides.

In contrast to traditional stacked waveguides, many embodiments of theinvention are directed to the manufacturing of multi-layered waveguideshaving alternating substrate layers and grating layers. Such waveguidescan be fabricated with an iterative process capable of sequentiallyforming grating layers for a single waveguide. In several embodiments,the multi-layered waveguide is fabricated with two grating layers. In anumber of embodiments, the multi-layered waveguide is fabricated withthree grating layers. Any number of grating layers can be formed,limited by the tools utilized and/or waveguide design. Compared totraditional multi-layered waveguides, this allows for a reduction inthickness, materials, and costs as fewer substrates are needed.Furthermore, the manufacturing process for such waveguides allow for ahigher yield in production due to simplified alignment and substratematching requirements.

Manufacturing processes for multi-layered waveguides having alternatingtransparent substrate layers and grating layers in accordance withvarious embodiments of the invention can be implemented using a varietyof techniques. In many embodiments, the manufacturing process includesdepositing a first layer of optical recording material onto a firsttransparent substrate. Optical recording material can include variousmaterials and mixtures, including but not limited to HPDLC mixtures andany of the material formulations discussed in the sections above.Similarly, any of a variety of deposition techniques, such as but notlimited to spraying, spin coating, inkjet printing, and any of thetechniques described in the sections above, can be utilized. Transparentsubstrates of various shapes, thicknesses, and materials can beutilized. Transparent substrates can include but are not limited toglass substrates and plastic substrates. Depending on the application,the transparent substrates can be coated with different types of filmsfor various purposes. Once the deposition process is completed, a secondtransparent substrate can then be placed onto the deposited first layerof optical recording material. In some embodiments, the process includesa lamination step to form the three-layer composite into a desiredheight/thickness. An exposure process can be implemented to form a setof gratings within the first layer of optical recording material.Exposure processes, such as but not limited to single-beaminterferential exposure and any of the other exposure processesdescribed in the sections above, can be utilized. In essence, asingle-layered waveguide is now formed. The process can then repeat toadd on additional layers to the waveguide. In several embodiments, asecond layer of optical recording material is deposited onto the secondtransparent substrate. A third transparent substrate can be placed ontothe second layer of optical recording material. Similar to the previoussteps, the composite can be laminated to a desired height/thickness. Asecond exposure process can then be performed to form a set of gratingswithin the second layer of optical recording material. The result is awaveguide having two grating layers. As can readily be appreciated, theprocess can continue iteratively to add additional layers. Theadditional optical recording layers can be added onto either side of thecurrent laminate. For instance, a third layer of optical recordingmaterial can be deposited onto the outer surface of either the firsttransparent substrate or the third transparent substrate.

In many embodiments, the manufacturing process includes one or more postprocessing steps. Post processing steps such as but not limited toplanarization, cleaning, application of protective coats, thermalannealing, alignment of LC directors to achieve a desired birefringencestate, extraction of LC from recorded SBGs and refilling with anothermaterial, etc. can be carried out at any stage of the manufacturingprocess. Some processes such as but not limited to waveguide dicing(where multiple elements are being produced), edge finishing, AR coatingdeposition, final protective coating application, etc. are typicallycarried out at the end of the manufacturing process.

In many embodiments, spacers, such as but not limited to beads and otherparticles, are dispersed throughout the optical recording material tohelp control and maintain the thickness of the layer of opticalrecording material. The spacers can also help prevent the two substratesfrom collapsing onto one another. In some embodiments, the waveguidecell is constructed with an optical recording layer sandwiched betweentwo planar substrates. Depending on the type of optical recordingmaterial used, thickness control can be difficult to achieve due to theviscosity of some optical recording materials and the lack of a boundingperimeter for the optical recording layer. In a number of embodiments,the spacers are relatively incompressible solids, which can allow forthe construction of waveguide cells with consistent thicknesses. Thespacers can take any suitable geometry, including but not limited torods and spheres. The size of a spacer can determine a localized minimumthickness for the area around the individual spacer. As such, thedimensions of the spacers can be selected to help attain the desiredoptical recording layer thickness. The spacers can take any suitablesize. In many cases, the sizes of the spacers range from 1 to 30 μm. Thespacers can be made of any of a variety of materials, including but notlimited to plastics (e.g., divinylbenzene), silica, and conductivematerials. In several embodiments, the material of the spacers isselected such that its refractive index does not substantially affectthe propagation of light within the waveguide cell.

In many embodiments, the first layer of optical recording material isincorporated between the first and second transparent substrates usingvacuum filling methods. In a number of embodiments, the layer of opticalrecording materials is separated in different sections, which can befilled or deposited as appropriate depending on the specificrequirements of a given application. In some embodiments, themanufacturing system is configured to expose the optical recordingmaterial from below. In such embodiments, the iterative multi-layeredfabrication process can include turning over the current device suchthat the exposure light is incident on a newly deposited opticalrecording layer before it is incident on any formed grating layers.

In many embodiments, the exposing process can include temporarily“erasing” or making transparent the previously formed grating layer suchthat they will not interfere with the recording process of the newlydeposited optical recording layer. Temporarily “erased” gratings orother optical structures can behave similar to transparent materials,allowing light to pass through without affecting the ray paths. Methodsfor recording gratings into layers of optical recording material usingsuch techniques can include fabricating a stack of optical structures inwhich a first optical recording material layer deposited on a substrateis exposed to form a first set of gratings, which can be temporarilyerased so that a second set of gratings can be recorded into a secondoptical recording material layer using optical recording beamstraversing the first optical recording material layer. Although therecording methods are discussed primarily with regards to waveguideswith two grating layers, the basic principle can be applied towaveguides with more than two grating layers.

Multi-layered waveguide fabrication processes incorporating steps oftemporarily erasing a grating structure can be implemented in variousways. Typically, the first layer is formed using conventional methods.The recording material utilized can include material systems capable ofsupporting optical structures that can be erased in response to astimulus. In embodiments in which the optical structure is a holographicgrating, the exposure process can utilize a crossed-beam holographicrecording apparatus. In a number of embodiments, the optical recordingprocess uses beams provided by a master grating, which may be a Bragghologram recorded in a photopolymer or an amplitude grating. In someembodiments, the exposure process utilizes a single recording beam inconjunction with a master grating to form an interferential exposurebeam. In addition to the processes described, other industrial processesand apparatuses currently used in the field to fabricate holograms canbe used.

Once a first set of gratings is recorded, additional material layers canbe added similar to the processes described above. During the exposureprocess of any material layer after the first material layer, anexternal stimulus can be applied to any previously formed gratings torender them effectively transparent. The effectively transparent gratinglayers can allow for light to pass through to expose the new materiallayer. External stimulus/stimuli can include optical, thermal, chemical,mechanical, electrical, and/or magnetic stimuli. In many embodiments,the external stimulus is applied at a strength below a predefinedthreshold to produce optical noise below a predefined level. Thespecific predefined threshold can depend on the type of material used toform the gratings. In some embodiments, a sacrificial alignment layerapplied to the first material layer can be used to temporarily erase thefirst set of gratings. In some embodiments, the strength of the externalstimulus applied to the first set of gratings is controlled to reducedoptical noise in the optical device during normal operation. In severalembodiments, the optical recording material further includes an additivefor facilitating the process of erasing the gratings, which can includeany of the methods described above. In a number of embodiments, astimulus is applied for the restoration of an erased layer.

The clearing and restoration of a recorded layer described in theprocess above can be achieved using many different methods. In manyembodiments, the first layer is cleared by applying a stimuluscontinuously during the recording of the second layer. In otherembodiments, the stimulus is initially applied, and the grating in thecleared layer can naturally revert to its recorded state over atimescale that allows for the recording of the second grating. In otherembodiments, the layer stays cleared after application of an externalstimulus and reverts in response to another external stimulus. Inseveral embodiments, the restoration of the first optical structure toits recorded state can be carried out using an alignment layer or anexternal stimulus. An external stimulus used for such restoration can beany of a variety of different stimuli, including but not limited to thestimulus/stimuli used to clear the optical structure. Depending on thecomposition material of the optical structure and layer to be cleared,the clearing process can vary. Further discussion regarding themulti-layered waveguide fabrication utilizing external stimuli can befound in U.S. application Ser. No. 16/522,491 filed Jul. 25, 2019entitled “Systems and Methods for Fabricating a Multilayer OpticalStructure.” The disclosure of U.S. application Ser. No. 16/522,491 ishereby incorporated by reference in its entirety for all purposes.

Waveguides Incorporating Integrated Gratings

Waveguides in accordance with various embodiments of the invention caninclude different grating configurations. In many embodiments, thewaveguide includes at least one input coupler and at least twointegrated gratings. In some embodiments, at least two integratedgratings can be implemented to work in combination to provide beamexpansion and beam extraction for light coupled into the waveguide bythe input coupler. Multiple integrated gratings can be implemented byoverlapping integrated gratings across different grating layers or bymultiplexing the integrated gratings. In a number of embodiments, theintegrated gratings are partially overlapped or multiplexed. Multiplexedgratings can include the superimposition of at least two gratings havingdifferent grating prescriptions within the same volume. Gratings havingdifferent grating prescriptions can have different grating vectorsand/or grating slant with respect to the waveguide's surface. Themagnitude of the grating vector of a grating can be defined as theinverse of the grating period while its direction can be defined as thedirection orthogonal to the fringes of the grating.

In several embodiments, an integrated can be implemented to perform bothbeam expansion and beam extraction. An integrated grating can beimplemented with one or more grating prescriptions. In a number ofembodiments, the integrated grating is implemented with at least twograting prescriptions. In further embodiments, the integrated grating isimplemented with at least three grating prescriptions. In manyembodiments, two grating prescriptions within the integrated gratinghave similar clock angles. In some embodiments, the two gratingprescriptions have different slant angles. An integrated grating inaccordance with various embodiments of the invention can be implementedusing a variety of types of gratings, such as but not limited to SRGs,SBGs, holographic gratings, and other types of gratings including thosedescribed in the sections above. In a number of embodiments, theintegrated grating includes two surface relief gratings. In otherembodiments, the integrated grating includes two holographic gratings.

The integrated grating can include at least two grating prescriptionsthat are at least partially overlapped or multiplexed. In furtherembodiments, the integrate grating includes at least two gratingprescriptions that are fully overlapped or multiplexed. In a number ofembodiments, the integrated grating includes multiplexed or overlappinggratings that have different sizes and/or shapes—i.e., one grating maybe larger than the other, resulting in only partial multiplexing of thelarger grating. As can readily be appreciated, various multiplexed andoverlapping configurations may be implemented as appropriate dependingon the specific requirements of a given application. Although thediscussions below may describe configurations as implementingmultiplexed or overlapping gratings, such gratings can be substitutedfor one another as appropriate depending on the application. In severalembodiments, the integrated gratings are implemented by a combination ofboth multiplexed and overlapping gratings. For example, two or more setsof multiplexed gratings can be overlapped across two or more gratinglayers.

Integrated gratings in accordance with various embodiments of theinvention can be utilized for various purposes including but not limitedto implementing full color waveguides and addressing some key problemsin conventional waveguide architectures. Other advantages includereduced material and waveguide refractive index requirements and reducedwaveguide dimensions resulting from the overlapping and/or multiplexingnature of the integrated gratings. Such configurations can allow forlarge field-of-view waveguides, which would ordinarily incurunacceptable increases in waveguide form factor and refractive indexrequirements. In many embodiments, a waveguide is implemented with atleast one substrate having a low refractive index. In some embodiments,the waveguide is implemented with a substrate having a refractive indexof lower than 1.8. In further embodiments, the waveguide is implementedwith a substrate having a refractive index of not more than ˜1.5.

Integrated gratings that can provide beam expansion and beamextraction—i.e., the functions of conventional fold and outputgratings—can result in a much smaller grating area, enabling a smallform factor and lower fabrication cost. By integrating the functions ofbeam expansion and extraction, instead of performing them serially as intraditional waveguides, beam expansion and extraction can beaccomplished with ˜50% of the grating interactions normally required,cutting down haze in the same proportion in the case of birefringentgratings. A further advantage is that, as a result of the greatlyshortened light paths, the number of beam bounces at glass/airinterface(s) is reduced, rendering the output image less sensitive tosubstrate nonuniformities. This can enable higher quality images and thepotential to use less expensive, lower specification substrates.

In many embodiments, the grating vectors of the input coupler andintegrated gratings are arranged to provide a substantially zeroresultant vector. The grating vectors of the input coupler andintegrated gratings can be arranged to form a triangular configuration.In several embodiments, the grating vectors can be arranged in anequilateral triangular configuration. In some embodiments, the gratingvectors can be arranged in an isosceles triangular configuration whereat least two grating vectors have equal magnitudes. In furtherembodiments, the grating vectors are arranged in an isosceles righttriangular configuration. In a number of embodiments, the gratingvectors are arranged in a scalene triangular configuration. Anotherwaveguide architecture includes integrated diffractive elements withgrating vectors aligned in the same direction for providing horizontalexpansion for one set of angles and extraction for a separate set ofangles. In several embodiments, one or more of the integrated gratingsare asymmetrical in their general shape. In some embodiments, one ormore of the integrated gratings has at least one axis of symmetry intheir general shape. In a number of embodiments, the gratings aredesigned to sandwich an electro-active material, enabling switchingbetween clear and diffracting states for certain types of gratings suchas but not limited to HPDLC gratings. The gratings can be a surfacerelief or a holographic type.

In many embodiments, a waveguide supporting at least one input couplerand first and second integrated gratings is implemented. The gratingstructures can be implemented in single- or multi-layered waveguidedesigns. In single-layered designs, the integrated gratings can bemultiplexed. In embodiments where each integrated grating contains atleast two multiplexed gratings, the multiplexed integrated gratings cancontain at least four multiplexed gratings. As described above, anyindividual multiplexed grating can be partially or completelymultiplexed with the other gratings. In some embodiments, amulti-layered waveguide is implemented with overlapping integratedgratings. In further embodiments, the integrated gratings are partiallyoverlapped. Each of the integrated gratings can be a separate grating ormultiplexed gratings.

In many embodiments, the waveguide architecture is designed to couplethe input light into two bifurcated paths using an input coupler. Suchconfigurations can be implemented in various ways. In some embodiments,a multiplexed input grating is implemented to couple input light intotwo bifurcated paths. In other embodiments, two input gratings areimplemented to separately couple input light into two bifurcated paths.The two input gratings can be implemented in the same layer orseparately in two layers. In a number of embodiments, two overlapping orpartially overlapping input gratings are implemented to couple inputlight into two bifurcated paths. In many embodiments, the input couplerincludes a prism. In further embodiments, the input coupler includes aprism and any of the input grating configuration described above.

In addition to various input coupler architectures, the first and secondintegrated gratings can be implemented in a variety of configurations.Integrated gratings in accordance with various embodiments of theinvention can be incorporated into waveguides to perform the dualfunction of two-dimensional beam expansion and beam extraction. Inseveral embodiments, the first and second integrated gratings arecrossed gratings. As described above, some waveguide architecturesinclude designs in which input light is coupled into two bifurcatedpaths. In such designs, the two bifurcated paths are each directedtowards a different integrated grating. As can readily be appreciated,such configurations can be designed to bifurcate the input light basedon various light characteristics, including but not limited to angularand spectral bandwidths. In some embodiments, light can be bifurcatedbased on polarization states—e.g., input unpolarized light can bebifurcated into S and P polarization paths. In many embodiments, each ofthe integrated gratings performs either beam expansion in a firstdirection or beam expansion in a second direction different from thefirst direction according to the field-of-view portion being propagatedthrough the waveguide. The first and second directions can be orthogonalto one another. In other embodiments, the first and second directionsare not orthogonal to one another. Each integrated grating can provideexpansion of the light in a first dimension while directing the lighttowards the other integrated grating, which provides expansion of thelight in a second dimension and extraction. For example, many gratingarchitectures in accordance with various embodiments of the inventioninclude an input configuration for bifurcating input light into firstand second portions of light. A first integrated grating can beconfigured to provide beam expansion in a first direction for the firstand second portions of light and to provide beam extraction for thesecond portion of light. Conversely, the second integrated grating canbe configured to provide beam expansion in a second direction for thefirst and second portions of light and to provide beam extraction forthe first portion of light.

In a number of embodiments, the first integrated grating includesmultiplexed first and second grating prescriptions, and the secondintegrated grating includes multiplexed third and fourth gratingprescriptions. In such embodiments, the first grating prescription canbe configured to provide beam expansion in a first direction for thefirst portion of light and to redirect the expanded light towards thefourth grating prescription. The second grating prescription can beconfigured to provide beam expansion in the first direction for thesecond portion of light and to extract the light out of the waveguide.The third grating prescription can be configured to provide beamexpansion in a second direction for the second portion of light and toredirect the expanded light towards the second grating prescription. Thefourth grating prescription can be configured to provide beam expansionin the second direction for the first portion of light and to extractthe light out of the waveguide. As can readily be appreciated, theintegrated gratings can be implemented with overlapping gratingprescriptions instead of multiplexed grating prescriptions. In manyembodiments, the first and second grating prescriptions have the sameclock angle but different grating slants. In some embodiments, the thirdand fourth grating prescriptions have the same clock angle, which isdifferent from the clock angles of the first and second gratingprescriptions. In a number of embodiments, the first, second, third, andfourth grating prescriptions all have different clock angles. In severalembodiments, the first, second, third, and fourth grating prescriptionsall have different grating periods. In a number of embodiments, thefirst and third grating prescriptions have the same grating period, andthe second and fourth grating prescriptions have the same gratingperiod.

FIG. 1 conceptually illustrates a waveguide display in accordance withan embodiment of the invention. As shown, the apparatus 100 includes awaveguide 101 supporting an input grating 102 and a grating structure103. Each grating can be characterized by a grating vector defining theorientation of the grating fringes in the plane of the waveguide. Agrating can also be characterized by a K-vector in 3D space, which inthe case of a Bragg grating is defined as the vector normal to thegrating fringes. The waveguide reflecting surfaces are parallel to theXY plane of the Cartesian reference frame inset into the drawing. Insome embodiments, the X and Y axes can correspond to global horizontaland vertical axes in the reference frame of a user of the display.

In the illustrative embodiment of FIG. 1, the input grating 102 includesa Bragg grating 104. In other embodiments, the input grating 102 is asurface relief grating. The input grating 102 can be implemented tobifurcate input light into two different portions. In furtherembodiments, the input grating 102 includes two multiplexed gratingshaving different grating prescriptions. In other embodiments, the inputgrating 102 includes two overlaid surface relief gratings. The gratingstructure 103 includes two effective gratings 105,106 that havedifferent grating vectors. The gratings 105,106 can be integratedgratings implemented as surface relief gratings or volume gratings. Inmany embodiments, the gratings 105,106 are multiplexed in a singlelayer. In several embodiments, the waveguide 101 provides two effectivegratings at all points across the grating structure 103 by overlayingmore than two separated gratings in the grating structure. For ease ofclarity, the gratings 105,106 that form the grating structure 103 willbe referred to as first and second integrated gratings since their rolein the grating structure includes providing beam expansion by changingthe direction of the guided beam in the plane of the waveguide and beamextraction. In various embodiments, the integrated gratings 105,106perform two-dimensional beam expansion and extraction of light from thewaveguide 101. The field-of-view coupled into the waveguide can bepartitioned into first and second portions, which can be bifurcated assuch by the input grating 102. In many embodiments, the first and secondportions correspond to positive and negative angles, vertically orhorizontally. In some embodiments, the first and second portions mayoverlap in angle space. In a number of embodiments, the first portion ofthe field-of-view is expanded in a first direction by the firstintegrated grating and, in a parallel operation, expanded in a seconddirection and extracted by the second integrated grating. When a rayinteracts with a grating fringe, some of the light that meets the Braggcondition is diffracted while non-diffracted light proceeds along itsTIR path up to the next fringe, continuing the expansion and extractionprocess. Considering next the second portion of the field-of-view, therole of the gratings is reversed such that the second portion of thefield is expanded in the second direction by the second integratedgrating and expanded in the first direction and extracted by the firstintegrated grating.

In many embodiments, the integrated gratings 105,106 in the gratingstructure 103 can be asymmetrically disposed. In some embodiments, theintegrated gratings 105,106 have grating vectors of differentmagnitudes. In several embodiments, the input grating 102 can have agrating vector offset from the Y-axis. In a number of embodiments, it isdesirable that the vector combination of the grating vectors of theinput grating 102 and the integrated gratings 105,106 in the gratingstructures 103 gives a resultant vector of substantially zero magnitude.As described above, the grating vectors can be arranged in anequilateral, isosceles, or scalene triangular configuration. Dependingon the application, certain configurations may be more desirable.

In many embodiments, at least one grating parameter selected from thegroup of grating vector direction, K-vector direction, gratingrefractive index modulation, and grating spatial frequency can varyspatially across at least one grating implemented in the waveguide forthe purposes of optimizing angular bandwidth, waveguide efficiency, andoutput uniformity to increase the angular response and/or efficiency. Insome embodiments, at least one of the gratings implemented in thewaveguide can employ rolled K-vectors—i.e., spatially varying K-vectors.In several embodiments, the spatial frequencies of the grating(s) arematched to overcome color dispersion.

The apparatus 100 of FIG. 1 further includes an input image generator.In the illustrative embodiment, the input image generator includes alaser scanning projector 107 that provides a scanned beam 107A over afield-of-view that is coupled into total internal reflection paths (TIRpaths) (108A,108B, for example) in the waveguide by the input grating102 and is directed towards the integrated gratings 105,106 to beexpanded and extracted (as shown by rays 109A,109B, for example). Insome embodiments, the laser projector 107 is configured to inject ascanned beam into the waveguide. In several embodiments, the laserprojector 107 can have a scan pattern modified to compensate for opticaldistortions in the waveguide. In a number of embodiments, the laserscanning pattern and/or grating prescriptions in the input grating 102and grating structure 103 can be modified to overcome illuminationbanding. In various embodiments, the laser scanning projector 107 can bereplaced by an input image generator based on a microdisplay illuminatedby a laser or an LED. In many embodiments, the input image can beprovided by an emissive display. A laser projector can offer theadvantages of improved color gamut, higher brightness, widerfield-of-view, high resolution, and a very compact form factor. In someembodiments, the apparatus 100 can further include a despeckler. Infurther embodiments, the despeckler can be implemented as a waveguidedevice. Although FIG. 1 shows a specific waveguide applicationimplementing integrated gratings, such structures and gratingarchitectures can be utilized for various applications. In a number ofembodiments, a waveguide having integrated gratings can be implementedin a single grating layer for a full color application. In manyembodiments, more than one grating layer implementing integratedgratings are implemented. Such configurations can be implemented toprovide wider angular or spectral bandwidth operation. In someembodiments, a multi-layered waveguide is implemented to provide a fullcolor application. In several embodiments, a multi-layered waveguide isimplemented to provide a wider field-of-view. In many embodiments, afull color waveguide having at least a ˜50° diagonal field-of-view isimplemented using integrated gratings. In some embodiments, a full colorwaveguide having at least a ˜100° diagonal field-of-view is implementedusing integrated gratings.

FIG. 2 conceptually illustrates a color waveguide display having twoblue-green diffracting waveguides and two green-red diffractingwaveguides in accordance with an embodiment of the invention. FIG. 2schematically illustrates an apparatus 200 with an architecture similarto that of FIG. 1 but includes the use of four stacked waveguides201A-201D, including two blue-green diffracting waveguides and twogreen-red diffracting waveguides. As shown, the apparatus 200 includes alaser scanning projector 202 that provides scanning beams 202A-202D. Inthe illustrative embodiment, the waveguides providing each color bandcan be configured to propagate different field-of-view portions. Forexample, in some embodiments, each of the waveguides operating in agiven color band provides a field-of-view of 35° h×35° v (50° diagonal),yielding 70° h×35° v (78° diagonal) field-of-view for each color bandwhen the two fields of view are combined. In many embodiments, thescanning beams can be generated using red, green, and blue laseremitters with each light of two laser wavelengths selected from red,green, and blue being injected into each waveguide according to thecolor band intended to be propagated by the waveguide. The laser beamintensities can be modulated for the purposed of color balancing. Thestacked waveguides can be arranged in any order. In several embodiments,consideration of factors such as but not limited to color crosstalk caninfluence the stack order. In a number of embodiments, the integratedgratings of one waveguide are partially or completely overlapped withthe integrated gratings of another waveguide. As described above, theintegrated gratings can be implemented in various configurations. Insome embodiments, the integrated gratings are implemented across morethan one grating layer. In several embodiments, each of the integratedgratings includes two multiplexed grating prescriptions.

In many embodiments, the optical geometrical requirements for combiningwaveguide paths for more than one field-of-view or color band candictate an asymmetric arrangement of the gratings used in the inputgrating(s) and the integrated gratings. In other words, the gratingvectors of the input grating and the integrated gratings are notequilaterally disposed or symmetrically disposed about the Y axis.

Although FIGS. 1 and 2 show specific configurations of waveguidearchitectures, various structures can be implemented as appropriatedepending on the specific requirements of a given application. In someembodiments, a six-layered waveguide is implemented for full colorapplications. The six-layered waveguide can be implemented with threepairs of layers configured for color bands of red, green, and blue,respectively. In such embodiments, waveguides within each pair can beconfigured for different field-of-view portions.

In some embodiments, to perform beam expansion and extraction, thewaveguide is designed such that each point of interaction of a ray witha grating structure occurs in a region of overlapping effectivegratings. In a non-fully overlapped grating configuration, the gratingstructures will have regions in which the first and second effectivegratings only partially overlap such that some rays interact with onlyone of the effective gratings. In many embodiments, the gratingstructures are formed from two multiplexed gratings. The first of themultiplexed grating 300, which is shown in FIG. 3A, multiplexes a firsteffective grating 301 with one 302 having a different effective gratingvector (or clock angle). The second multiplexed grating 310, which isshown in FIG. 3B, multiplexes a second effective grating 311 with one312 having a different effective grating vector. FIGS. 3A-3B areintended to illustrate the relative orientations of the multiplexedgratings and do not represent the shapes of the gratings as implemented.In some embodiments, the gratings 301,302 and 311,312 may differ inshape from each other. In the embodiments of FIGS. 3A-3B, the gratingvector (clock angle) of the second multiplexed grating is identical tothe first grating vector of the first multiplexed grating. Likewise, thegrating vector of the first multiplexed grating is identical to thesecond grating vector of the second multiplexed grating. Turning now toFIG. 3C, it should be apparent that when the gratings are overlapped320, there are two gratings of different clock angles at any point inthe grating structures (e.g., in the regions of partial overlap—labeledby numerals 2-4 in FIG. 3C) of the effective gratings. In the regions offull overlap (labelled by numeral 1 in FIG. 3C) of the effectivegratings, there will be four gratings overlapping any point in thegrating structures. However, in such regions, each pair of gratingshaving the same clock angle results in only two overlapping effectivegratings. It should be appreciated from the above description that, inmany embodiments, the two pairs of multiplexed gratings could beimplemented as one multiplexed grating formed from the four gratings301,302 and 311, 312.

FIGS. 4A-4C schematically illustrate ray propagation through a gratingstructure 400 having an input grating 401 and two integrated gratings402,403 in accordance with an embodiment of the invention. The raypropagation is illustrated using unfolded ray paths to clarify theinteraction between the rays and gratings. As shown in the schematicdiagram of FIG. 4A, light from a first portion of the FOV shows a ray404A coupled into a TIR path in the waveguide by the input grating 401,a TIR ray 405A leading to the first integrated grating 402, a TIR ray406A diffracted by the first integrated grating 403 (which also providesbeam expansion in a first direction), and a ray 407A diffracted out ofthe waveguide by the second integrated grating 403 (which also providesbeam expansion in a second direction). Turning now to the propagation ofthe second portion of the FOV, which is shown in FIG. 4B, the ray pathincludes a ray 404B coupled into a TIR path in the waveguide by theinput grating 401, a TIR ray 405B leading to the second integratedgrating 403, a TIR ray 406B diffracted by the second integrated grating403 (which also provides beam expansion in the second direction), and aTIR ray 407B diffracted out of the waveguide by the first integratedgrating 402 (which also provides beam expansion in the first direction).FIG. 4C shows the combined paths of FIGS. 4A-4B with the integratedgratings overlaid. FIG. 4C also shows the partial overlapping nature ofthe integrated gratings along the paths of the rays. As can readily beappreciated, such configurations can be modified as appropriatedepending on the specific requirements of a given application. Gratingsof various shapes can be utilized. An integrated grating can include twomultiplexed gratings, one providing the function of a traditional foldgrating and another for extracting the light similar to a traditionaloutput grating. Each of the two multiplexed gratings within a singleintegrated grating can be configured to act on different portions oflight bifurcated by the input configuration. In a number of embodiments,the two multiplexed gratings within a single integrated grating can havedifferent shapes—i.e., certain areas of one or both of the gratings arenot multiplexed. In some embodiments, more than two gratings aremultiplexed for a single integrated grating. In many embodiments, theintegrated gratings are multiplexed in a single grating layer. Inseveral embodiments, the integrated gratings are fully multiplexed oroverlapped. In other embodiments, only portions of the integratedgratings are multiplexed overlapped.

As described above, grating architectures including those implementingintegrated gratings can be described and visualized using gratingvectors. In many embodiments, three grating vectors, which can representtraditional input, fold, and output functions, can be implemented with asubstantially zero resultant vector. FIG. 5A conceptually illustrates agrating vector configuration with a substantially zero resultant vectorin accordance with an embodiment of the invention. As shown, theconfiguration 500 includes three grating vectors 501-503 represented ask₁, k₂, and k₃, respectively. With three grating vectors, configurationshaving a substantially zero resultant vector can provide varioustriangular configurations, such as but not limited to equilateraltriangles, isosceles triangles, and scalene triangles. In the case ofarchitectures utilizing integrated gratings, more than one triangularconfiguration can be visualized. FIG. 5B conceptually illustrates onesuch embodiment. As shown, the configuration 510 illustrates twotriangular configurations. One triangular configuration is formed bygrating vectors k₁, k₂, and k₃ (511-513), and a second configuration isformed by grating vectors k₁, k₄, and k₅ (511, 514, and 515). In theillustrative embodiment, grating vector k₁ represents the function ofthe input coupler, grating vectors k₂ and k₅ represent the functions ofa first integrated grating, and grating vectors k₄ and k₃ represent thefunctions of a second integrated grating.

In many embodiments, the grating vector configuration implemented caninclude various triangular configurations. Typically, the magnitudes ofthe grating vectors can dictate the resulting triangular configuration.In some embodiments, an equilateral triangular configuration isimplemented where all grating vectors are of similar, or substantiallysimilar, magnitude. In cases where integrated gratings are implemented,the configuration can include two triangular configurations. In a numberof embodiments, the grating vector configuration includes at least oneisosceles triangle where at least two of the grating vectors havesimilar, or substantially similar, magnitudes. FIG. 5C conceptuallyillustrates a grating vector configuration with two isosceles trianglesin accordance with an embodiment of the invention. As shown, theconfiguration 520 forms two isosceles triangles due to grating vectorsk₂-k₅ having similar magnitudes. In several embodiments, the gratingconfiguration includes at least one scalene triangle. FIG. 5Dconceptually illustrates a grating vector configuration with two scalenetriangles in accordance an embodiment of the invention. As shown, theconfiguration 530 forms two scalene triangles. In the illustrativeembodiment, the two scalene triangles are mirrored—i.e., grating vectorsk₂ and k₄ are equal in magnitude, and grating vectors k₃ and k₅ areequal in magnitude. FIG. 5E conceptually illustrates a grating vectorconfiguration with two different scalene triangles in accordance with anembodiment of the invention. As shown, the configuration 540 includestwo different scalene triangles with grating vectors k₂-k₅ havingdifferent magnitudes.

Although FIGS. 5A-5E illustrate specific grating vector configurations,various other configurations can be implemented as appropriate dependingon the specific requirements of a given application. For example, insome embodiments, the input coupler is implemented to have two differentgrating vectors. Such configurations utilize an input grating having twodifferent grating prescriptions, which can implemented using overlappingor multiplexed grating prescriptions. In the embodiments illustrated inFIGS. 5B-5E, the configurations shown can be due to the implementationof integrated gratings. In many embodiments, grating vectors k₂ and k₅represent the functions of a first integrated grating, and gratingvectors k₄ and k₃ represent the functions of a second integratedgrating. In several embodiments, each grating vector k₁ represent adifferent grating prescription. For example, many grating architecturesin accordance with various embodiments of the invention can implementintegrated gratings that each contain two different gratingprescriptions. In such cases, grating vectors k₂ and k₅ can respectivelyrepresent the two different grating prescriptions of a first integratedgrating, and grating vectors k₄ and k₃ can respectively represent thetwo different grating prescriptions of a second integrated grating.

FIG. 6 conceptually illustrates a schematic plan view of a gratingarchitecture 600 having an input grating and integrated gratings inaccordance with an embodiment of the invention. As shown, the gratingarchitecture 600 includes an input coupler 601. The input coupler 601can be a Bragg grating or a surface relief grating. In many embodiments,the input coupler 601 includes at least two gratings. In suchembodiments, individual input gratings can be configured to couple indifferent portions of input light, which can be based on angular orspectral characteristics. In some embodiments, the input couple 601includes two overlapped gratings. In other embodiments, the inputcoupler 601 includes two multiplexed gratings. The grating architecture600 further includes first (bold lines) and second (dashed lines)integrated gratings. In the illustrative embodiment, the firstintegrated grating includes a first grating 602 having a first gratingprescription and a second grating 603 having a second gratingprescription. As shown, the second grating 603 is smaller than the firstgrating 602 and can be entirely multiplexed within the volume of thefirst grating 602. In some embodiments, the first and second gratings602,603 are overlapped across different grating layers. In severalembodiments, the first and second gratings 602,603 are adjacent ornearly adjacent one another and are neither overlapped nor multiplexed.In a number of embodiments, the first and second gratings 602,603 havethe same clock angles but different grating prescriptions.

In many embodiments, the configuration of the first integrated gratingis applied similarly to the second integrated grating but flipped aboutan axis. For example, the illustrative embodiment in FIG. 6 shows thesecond integrated grating having third 604 and fourth 605 gratings withshapes corresponding to the first and second gratings 602,603,respectively. The third grating 604 has a third grating prescription,and the fourth grating 605 has a fourth grating prescription. Similar tothe first integrated grating, the third and fourth gratings 604,605 canhave the same clock angles but different grating prescriptions. In anumber of embodiments, the first and second gratings 602,603 are clockedat an angle different from the third and fourth gratings 604,605. Again,the overlapping and multiplexing nature of the third and fourth gratings604,605 can be implemented in a similar manner as the first and secondgratings 602,603.

In the illustrative embodiment of FIG. 6, the first and third integratedgratings are partially overlapped with one another such that the secondand fourth gratings 603,605 are also partially overlapped. In theillustrative embodiment, the second and fourth gratings 603,605 aremultiplexed within the first and third gratings 602,604, and, as such,the waveguide architecture includes an area 606 where four gratingprescriptions are active. In embodiments where the first and secondintegrated gratings are implemented in a single layer, area 606 wouldcontain four multiplexed gratings. In other embodiments, the first andsecond integrated gratings are implemented across different gratinglayers.

During operation, input light incident on the input grating 601 can bebifurcated into two portions of light traveling in TIR paths within thewaveguide. One portion can be directed towards the first grating 602while the other portion can be directed towards the third grating 604.The first grating 602 can be configured to provide beam expansion in afirst direction for incident light and to redirect the incident lighttowards the fourth grating 605. The fourth grating 605 can be configuredto provide beam expansion in a second direction for incident light andto extract the light out of the waveguide. On the other hand, the thirdgrating 604 can be configured to provide beam expansion in the seconddirection for incident light and to redirect the incident light towardsthe second grating 603. The second grating 603 can be configured toprovide beam expansion in the first direction for incident light and toextract the light out of the waveguide.

FIG. 7 shows a flow diagram conceptually illustrating a method ofdisplaying an image in accordance with an embodiment of the invention.Referring to the flow diagram, the method 700 includes providing (701) awaveguide supporting an input grating, a first integrated grating, and asecond integrated grating. In many embodiments, the first integratedgrating partially overlaps the second integrated grating. In someembodiments, the integrated gratings are fully overlapped. The first andsecond integrated gratings can include multiplexed pairs of differentK-vector gratings. A first field-of-view portion can be coupled (702)into the waveguide via the input grating and directed towards the firstintegrated grating. A second field-of-view portion can be coupled (703)into the waveguide via the input grating and directed towards the secondintegrated grating. The first field-of-view portion light can beexpanded (704) in a first direction using the first integrated grating.The first field-of-view portion light can be expanded in a seconddirection and extracted (705) from the waveguide using the secondintegrated grating. The second field-of-view portion light can beexpanded in the second direction (706) using the second integratedgrating. The second field-of-view portion light can be expanded in thefirst direction and extracted (707) from the waveguide using the firstintegrated grating.

As described in the sections above, integrated gratings can beimplemented in a variety of different ways. In many embodiments, anintegrated grating is implemented with two gratings that have the sameclock angle but different grating prescriptions. In further embodiments,the two gratings are multiplexed. FIG. 8 shows a flow diagramconceptually illustrating a method of displaying an image utilizingintegrated gratings containing multiple gratings in accordance with anembodiment of the invention. Referring to the flow diagram, the method800 includes providing (801) a waveguide supporting an input grating,first and second gratings having a first clock angle, and third andfourth gratings having a second clock angle, where the first and thirdgrating at least partially overlaps. In many embodiments, the firstintegrated grating partially overlaps the second integrated grating. Insome embodiments, the integrated gratings are fully overlapped. Thefirst and second integrated gratings can include multiplexed pairs ofdifferent K-vector gratings. A first field-of-view portion can becoupled (802) into the waveguide via the input grating and directedtowards the first grating. A second field-of-view portion can be coupled(803) into the waveguide via the input grating and directed towards thethird grating. The first field-of-view portion light can be expanded(804) in a first direction using the first grating and redirectedtowards the fourth grating. The first field-of-view portion light can beexpanded in a second direction and extracted (805) from the waveguideusing the fourth grating. The second field-of-view portion light can beexpanded in the second direction (806) using the third grating andredirected towards the second grating. The second field-of-view portionlight can be expanded in the first direction and extracted (807) fromthe waveguide using the second grating.

Although FIGS. 6-8 illustrate specific waveguide configurations andmethods of displaying an image, many different methods can beimplemented in accordance with various embodiments of the invention. Forexample, in some embodiments, more than one input grating is utilized.In other embodiments, the input configuration includes a prism. Suchmethods and implemented waveguides can also be configured to improveperformance and/or provide various different functions. In manyembodiments, the waveguide apparatus includes at least one grating withspatially-varying pitch. In some embodiments, each grating has a fixed Kvector. In a number of embodiments, at least one of the gratings is arolled k-vector grating according to the embodiments and teachingsdisclosed in the cited references. Rolling the K-vectors can allow theangular bandwidth of the grating to be expanded without the need todecrease the grating thickness or to utilize multiple grating layers. Insome embodiments a rolled K-vector grating includes a waveguide portioncontaining discrete grating elements having differently alignedK-vectors. In some embodiments, a rolled K-vector grating comprises awaveguide portion containing a single grating element within which theK-vectors undergo a smooth monotonic variation in direction. In some ofthe embodiments describe rolled K-vector gratings are used to inputlight into the waveguide. In some embodiments, waveguides having twointegrated gratings can be implemented as single-layered ormulti-layered waveguides. In several embodiments, a multi-layeredwaveguide is implemented with more than two integrated gratings. As canreadily be appreciated, the specific architecture and configurationimplemented can depend on a number of different factors. In someembodiments, the position of the input grating relative to theintegrated gratings can be dictated by various factors, including butnot limited to projector relief and the input pupil diameter andvergence. In many applications, it is desirable for the distance betweenthe input grating and the integrated gratings to be minimized to providea waveguide having a small form factor. The field ray angle pathsrequired to fill the eyebox typically dominate the waveguide height. Inmany cases, the height of waveguide grows non-linearly with projectorrelief. In some embodiments, the pupil diameter does not have asignificant impact on the footprint of the waveguide. A converging ordiverging pupil can be used to reduce the local angle response at anylocation on the input grating.

In some embodiments, the waveguide configuration implemented can dependon the configuration of the input image generator/projector. FIG. 9conceptually illustrates a profile view 900 of two overlapping waveguideportions implementing integrated gratings in accordance with anembodiment of the invention. In the illustrative embodiment, thetwo-layered waveguide is designed for a high field-of-view applicationimplemented with a converging projector pupil input beam, indicated byrays 901. As shown, the apparatus includes a first waveguide 902containing a first grating layer 903 having a first set of twointegrated gratings and a second waveguide 904 containing a secondgrating layer 905 having a second set of two integrated gratings thatpartially overlaps the first set of two integrated gratings. The gratinglayers 903,905 having integrated gratings can operate according to theprinciples discussed in the sections above. The output beam from thewaveguides is generally indicated by rays 906 intersecting the eyebox907. In the illustrated embodiment, the eyebox has dimensions 10.5mm.×9.5 mm., an eye relief of 13.5 mm, and a laser projector towaveguide separation of 12 mm. As can readily be appreciated, suchdimensions and specifications can be specifically tailored depending onthe requirements of a given application.

FIG. 10 conceptually illustrates a schematic plan view 1000 of a gratingarchitecture having two sets of integrated gratings in accordance withan embodiment of the invention. As shown, the grating configurationincludes first and second input gratings 1001,1002, forming the combinedinput grating area 1003 indicated by the shaded area. In someembodiments, each of the input gratings includes a set of multiplexed oroverlapping gratings. The grating configuration further includes a firstset of grating structures having first and second integrated gratings1004,1005 and a second set of grating structures having third and fourthintegrated gratings 1006,1007. In the illustrative embodiment, each setof integrated gratings is shaped and disposed asymmetrically. Suchconfigurations can be implemented as appropriate depending on severalfactors. In the embodiment of FIG. 10, the asymmetrical gratingarchitecture can be implemented for operation with a convergingprojector pupil configuration, such as the one shown in FIG. 9.Furthermore, different grating characteristics can be implemented andtuned for different applications. FIG. 11 conceptually illustrates aplot 1100 of diffraction efficiency versus angle for a waveguide fordiffractions occurring at different field-of-view angles in accordancewith an embodiment of the invention. As shown, the waveguide is tuned tohave three different peak diffraction efficiencies, with two differentpeaks 1101,1102 for the “fold” interaction and one 1103 for the“output.” In some embodiments, light undergoes a dual interaction withinthe grating. Such gratings can be designed to have high diffractionefficiencies for two different incident angles. Turning back to FIG. 10,the first and second set of grating structures can be implemented aspartially overlapping structures, forming a combined output grating area1008 as indicated by the shaded area. The eyebox 1009 is overlaid on thedrawing and is indicated by the dark shaded area. In the illustrativeembodiment, the waveguide apparatus is configured to provide a FOV of120 degrees diagonal. As shown in FIGS. 9-10, in some embodiments,displays providing a FOV of 120 degrees diagonal can be configured witha projector to waveguide distance of 12 mm and an eye relief of 13.5mm., which is compatible with many glasses inserts. In some embodiments,the display provides an eyebox of 10.5 mm.×9.5 mm., which can provideeasy wearability. FIG. 12 shows the viewing geometry of such awaveguide. As can readily be appreciated, the grating configurationillustrated by FIG. 10 can be implemented in a variety of waveguidearchitectures. In some embodiments, both input gratings and both sets ofgrating structures are implemented in a single grating layer, with theoverlapping portions multiplexed. In several embodiments, the firstinput grating and the first set of grating structures are implemented ina first grating layer while the second input grating and the second setof grating structures are implemented in a second grating layer. In anumber of embodiments, the first, second, third, and fourth integratedgratings are implemented across four grating layers.

FIG. 13 conceptually illustrates the field-of-view geometry for abinocular display with binocular overlap between the left and right eyeimages provided by a waveguide in accordance with an embodiment of theinvention. Binocular displays utilizing various grating architectures,such as the one described in FIGS. 9-10. can be implemented. In theillustrated embodiment, the waveguide is a color waveguide that includesa stack of four waveguides: two blue-green layers and two green-redlayers. Each of the waveguides can provide a field-of-view of 35° h×35°v (˜50° diagonal) for a single-color band, yielding 70° h×35° v (˜78°diagonal) field-of-view for each color band. Each waveguide set for theleft and right eyes can be overlapped by 50° horizontally to achieve˜100° diagonal binocular field-of-view. As can readily be appreciated,various binocular configurations can be implemented as appropriateddepending on the specific requirements of a given application. In manyembodiments, the waveguide is raked at an angle of at least 5°, whichcan facilitate the implementation of some binocular overlappedfield-of-view applications. In further embodiments, the waveguide israked at an angle of at least 10°. In some embodiments, thefield-of-views for both the left and right eyes are completelyoverlapped.

Other Waveguide Embodiments

In some embodiments, a prism may be used as an alternative to the inputgrating. In many embodiments, this can require that an external gratingis provided for grating vector closure purposes. In several embodiments,the external grating may be disposed on the surface of the prism. Insome embodiments, the external grating may form part of a laserdespeckler disposed in the optical train between the laser projector andthe input prims. The use of a prism to couple light into a waveguide hasthe advantage of avoiding the significant light loss and restrictedangular bandwidth resulting from the use of a rolled K-vector grating. Apractical rolled K-vector input grating typically cannot match the muchlarge angular bandwidth of the fold grating, which can be around 40degrees or more.

Although the drawings may indicate a high degree of symmetry in thegrating geometry and layout of the gratings in the different wavelengthchannels, the grating prescriptions and footprints can be asymmetric.The shapes of the input, fold, or output gratings can depend on thewaveguide application and could be of any polygonal geometry subject tofactors such as the required beam expansion, output beam geometry, beamuniformity, and ergonomic factors.

In some embodiments, directed at displays using unpolarized lightsources, the input gratings can combine gratings orientated such thateach grating diffracts a particular polarization of the incidentunpolarized light into a waveguide path. Such embodiments mayincorporate some of the embodiments and teachings disclosed in the PCTapplication PCT/GB2017/000040 “METHOD AND APPARATUS FOR PROVIDING APOLARIZATION SELECTIVE HOLOGRAPHIC WAVGUIDE DEVICE” by Waldern et al.,the disclosure of which is incorporated herein in by reference in itsentirety. The output gratings can be configured in a similar fashion sothat the light from the waveguide paths is combined and coupled out ofthe waveguide as unpolarized light. For example, in some embodiments,the input grating and output grating each combine crossed gratings withpeak diffraction efficiency for orthogonal polarizations states. In anumber of embodiments, the polarization states are S-polarized andP-polarized. In several embodiments, the polarization states areopposing senses of circular polarization. The advantage of gratingsrecorded in liquid crystal polymer systems, such as SBGs, in this regardis that owing to their inherent birefringence, they exhibit strongpolarization selectivity. However, other grating technologies that canbe configured to provide unique polarization states can also be used.

In some embodiments using gratings recorded in liquid crystal polymermaterial systems, at least one polarization control layer overlapping atleast one of the fold gratings, input gratings, or output gratings maybe provided for the purposes of compensating for polarization rotationin any the gratings, particularly the fold gratings, which can result inpolarization rotation. In many embodiments, all of the gratings areoverlaid by polarization control layers. In a number of embodiments,polarization control layers are applied to the fold gratings only or toany other subset of the gratings. The polarization control layer mayinclude an optical retarder film. In some embodiments based on HPDLCmaterials, the birefringence of the gratings may be used to control thepolarization properties of the waveguide device. The use of thebirefringence tensor of the HPDLC grating, K-vectors, and gratingfootprints as design variables opens up the design space for optimizingthe angular capability and optical efficiency of the waveguide device.In some embodiments, a quarter wave plate can be disposed on a glass-airinterface of the wave guide rotates polarization of a light ray tomaintain efficient coupling with the gratings. In further embodiments,the quarter wave plate is a coating that is applied to substratewaveguide. In some waveguide display embodiments, applying a quarterwave coating to a substrate of the waveguide may help light rays retainalignment with the intended viewing axis by compensating for skew wavesin the waveguide. In some embodiments, the quarter wave plate may beprovided as a multi-layer coating.

As used in relation to any of the embodiments described herein, the termgrating may encompass a grating that includes a set of gratings. Forexample, in some embodiments, the input grating and output grating eachinclude two or more gratings multiplexed into a single layer. It is wellestablished in the literature of holography that more than oneholographic prescription can be recorded into a single holographiclayer. Methods for recording such multiplexed holograms are well knownto those skilled in the art. In some embodiments, the input grating andoutput grating may each include two overlapping gratings layers that arein contact or vertically separated by one or more thin opticalsubstrate. In several embodiments, the grating layers are sandwichedbetween glass or plastic substrates. In a number of embodiments, two ormore such gratings layers may form a stack within which total internalreflection occurs at the outer substrate and air interfaces. In someembodiments, the waveguide may include just one grating layer. In manyembodiments, electrodes may be applied to faces of the substrates toswitch gratings between diffracting and clear states. The stack mayfurther include additional layers such as beam splitting coatings andenvironmental protection layers.

In some embodiments, the fold grating angular bandwidth can be enhancedby designing the grating prescription to facilitate dual interaction ofthe guided light with the grating. Exemplary embodiments of dualinteraction fold gratings are disclosed in U.S. patent application Ser.No. 14/620,969 entitled “WAVEGUIDE GRATING DEVICE.”

Advantageously, to improve color uniformity, gratings for use in theinvention can be designed using reverse ray tracing from the eyebox tothe input grating via the output grating and fold grating. This processallows the required physical extent of the gratings, in particular thefold grating, to be identified. Unnecessary grating real-state whichcontribute to haze can be eliminated. Ray paths can be optimized forred, green, and blue, each of which follow slightly different pathsbecause of dispersion effects between the input and output gratings viathe fold grating.

In many embodiments, the gratings are holographic gratings, such as aswitchable or non-switchable Bragg Gratings. In some embodiments,gratings embodied as SBGs can be Bragg gratings recorded in aholographic polymer dispersed liquid crystal (e.g., a matrix of liquidcrystal droplets), although SBGs may also be recorded in othermaterials. In several embodiments, the SBGs are recorded in a uniformmodulation material, such as POLICRYPS or POLIPHEM having a matrix ofsolid liquid crystals dispersed in a liquid polymer. The SBGs can beswitching or non-switching in nature. In some embodiments, at least oneof the input, fold, and output gratings may be electrically switchable.In many embodiments, it is desirable that all three grating types arepassive, that is, non-switching. In its non-switching form, an SBG hasthe advantage over conventional holographic photopolymer materials ofbeing capable of providing high refractive index modulation due to itsliquid crystal component. Exemplary uniform modulation liquidcrystal-polymer material systems are disclosed in United State PatentApplication Publication No.: US2007/0019152 by Caputo et al and PCTApplication No.: PCT/EP2005/006950 by Stumpe et al., both of which areincorporated herein by reference in their entireties. Uniform modulationgratings are characterized by high refractive index modulation (andhence high diffraction efficiency) and low scatter. In some embodiments,the input coupler, the fold grating, and the output grating are recordedin a reverse mode HPDLC material. Reverse mode HPDLC differs fromconventional HPDLC in that the grating is passive when no electric fieldis applied and becomes diffractive in the presence of an electric field.The reverse mode HPDLC may be based on any of the recipes and processesdisclosed in PCT Application No.: PCT/GB2012/000680, entitled“IMPROVEMENTS TO HOLOGRAPHIC POLYMER DISPERSED LIQUID CRYSTAL MATERIALSAND DEVICES.” The gratings may be recorded in any of the above materialsystems but used in a passive (non-switching) mode. The advantage ofrecording a passive grating in a liquid crystal polymer material is thatthe final hologram benefits from the high index modulation afforded bythe liquid crystal. Higher index modulation translates to highdiffraction efficiency and wide angular bandwidth. The fabricationprocess is identical to that used for switched but with the electrodecoating stage being omitted. LC polymer material systems are highlydesirable in view of their high index modulation. In some embodiments,the gratings are recorded in HPDLC but are not switched.

In many embodiments, two spatially separated input couplers may be usedto provide two separate waveguide input pupils. In some embodiments, theinput coupler is a grating. In several embodiments, the input coupler isa prism. In embodiments using an input coupler prism based on prismsonly, the conditions for grating reciprocity can be addressed using thepitch and clock angles of the fold and output gratings.

In many embodiments, the source of data modulated light used with theabove waveguide embodiments includes an Input Image Node (“IIN”)incorporating a microdisplay. The input grating can be configured toreceive collimated light from the IIN and to cause the light to travelwithin the waveguide via total internal reflection between the firstsurface and the second surface to the fold grating. Typically, the IINintegrates, in addition to the microdisplay panel, a light source andoptical components needed to illuminate the display panel, separate thereflected light, and collimate it into the required FOV. Each imagepixel on the microdisplay can be converted into a unique angulardirection within the first waveguide. The instant disclosure does notassume any particular microdisplay technology. In some embodiments, themicrodisplay panel can be a liquid crystal device or a MEMS device. Inseveral embodiments, the microdisplay may be based on Organic LightEmitting Diode (OLED) technology. Such emissive devices would notrequire a separate light source and would therefore offer the benefitsof a smaller form factor. In some embodiments, the IIN may be based on ascanned modulated laser. The IIN projects the image displayed on themicrodisplay panel such that each display pixel is converted into aunique angular direction within the substrate waveguide according tosome embodiments. The collimation optics contained in the IIN mayinclude lens and mirrors, which may be diffractive lenses and mirrors.In some embodiments, the IIN may be based on the embodiments andteachings disclosed in U.S. patent application Ser. No. 13/869,866entitled “HOLOGRAPHIC WIDE-ANGLE DISPLAY,” and U.S. patent applicationSer. No. 13/844,456 entitled “TRANSPARENT WAVEGUIDE DISPLAY.” In severalembodiments, the IIN contains beamsplitter for directing light onto themicrodisplay and transmitting the reflected light towards the waveguide.In many embodiments, the beamsplitter is a grating recorded in HPDLC anduses the intrinsic polarization selectivity of such gratings to separatethe light illuminating the display and the image modulated lightreflected off the display. In some embodiments, the beam splitter is apolarizing beam splitter cube. In a number of embodiments, the IINincorporates a despeckler. The despeckler can be a holographic waveguidedevice based on the embodiments and teachings of U.S. Pat. No. 8,565,560entitled “LASER ILLUMINATION DEVICE.” The light source can be a laser orLED and can include one or more lenses for modifying the illuminationbeam angular characteristics. The image source can be a micro-display orlaser-based display. LED can provide better uniformity than laser. Iflaser illumination is used, there is a risk of illumination bandingoccurring at the waveguide output. In some embodiments, laserillumination banding in waveguides can be overcome using the techniquesand teachings disclosed in U.S. Provisional Patent Application No.:62/071,277 entitled “METHOD AND APPARATUS FOR GENERATING INPUT IMAGESFOR HOLOGRAPHIC WAVEGUIDE DISPLAYS.” In some embodiments, the light fromthe light source is polarized. In one or more embodiments, the imagesource is a liquid crystal display (LCD) micro display or liquid crystalon silicon (LCoS) micro display.

The principles and teachings of the invention in combination with otherwaveguide inventions by the inventors as disclosed in the referencedocuments incorporated by reference herein may be applied in manydifferent display and sensor devices. In some embodiments directed atdisplays, a waveguide display according to the principles of theinvention can be combined with an eye tracker. In some embodiments, theeye tracker is a waveguide device overlaying the display waveguide andis based on the embodiments and teachings of PCT/GB2014/000197 entitled“HOLOGRAPHIC WAVEGUIDE EYE TRACKER,” PCT/GB2015/000274 entitled“HOLOGRAPHIC WAVEGUIDE OPTICALTRACKER,” and PCT ApplicationNo.:GB2013/000210 entitled “APPARATUS FOR EYE TRACKING.”

In some embodiments of the invention directed at displays, a waveguidedisplay according to the principles of the invention further includes adynamic focusing element. The dynamic focusing element may be based onthe embodiments and teachings of U.S. Provisional Patent ApplicationNo.: 62/176,572 entitled “ELECTRICALLY FOCUS TUNABLE LENS.” In someembodiments, a waveguide display according to the principles of theinvention can further include a dynamic focusing element and an eyetracker, which can provide a light field display based on theembodiments and teachings disclosed in U.S. Provisional PatentApplication No.: 62/125,089 entitled “HOLOGRAPHIC WAVEGUIDE LIGHT FIELDDISPLAYS.”

In some embodiments of the invention directed at displays, a waveguideaccording to the principles of the invention may be based on some of theembodiments of U.S. patent application Ser. No. 13/869,866 entitled“HOLOGRAPHIC WIDEANGLE DISPLAY,” and U.S. patent application Ser. No.13/844,456 entitled “TRANSPARENT WAVEGUIDE DISPLAY.” In someembodiments, a waveguide apparatus according to the principles of theinvention may be integrated within a window, for example awindscreen-integrated HUD for road vehicle applications. In someembodiments, a window-integrated display may be based on the embodimentsand teachings disclosed in U.S. Provisional Patent Application No.: PCTApplication No.: PCT/GB2016/000005 entitled “ENVIRONMENTALLY ISOLATEDWAVEGUIDE DISPLAY.” In some embodiments, a waveguide apparatus mayinclude gradient index (GRIN) wave-guiding components for relaying imagecontent between the IIN and the waveguide. Exemplary embodiments aredisclosed in PCT Application No.: PCT/GB2016/000005 entitled“ENVIRONMENTALLY ISOLATED WAVEGUIDE DISPLAY.” In some embodiments, thewaveguide apparatus may incorporate a light pipe for providing beamexpansion in one direction based on the embodiments disclosed in U.S.Provisional Patent Application No.: 62/177,494 entitled “WAVEGUIDEDEVICE INCORPORATING A LIGHT PIPE.”

In many embodiments, a waveguide according to the principles of theinvention provides an image at infinity. In some embodiments, the imagemay be at some intermediate distance. In some embodiments, the image maybe at a distance compatible with the relaxed viewing range of the humaneye. In many embodiments, this may cover viewing ranges from about 2meters up to about 10 meters.

The construction and arrangement of the systems and methods as shown inthe various exemplary embodiments are illustrative only. Although only afew embodiments have been described in detail in this disclosure, manymodifications are possible (for example, variations in sizes,dimensions, structures, shapes and proportions of the various elements,values of parameters, mounting arrangements, use of materials, colors,orientations, etc.). For example, the position of elements may bereversed or otherwise varied, and the nature or number of discreteelements or positions may be altered or varied. The present inventioncan incorporate the embodiments and teachings disclosed in U.S.Provisional Patent Application No. 62/778,239 “METHODS AND APPARATUSESFOR PROVIDING A SINGLE GRATING LAYER COLOR HOLOGRAPHIC WAVEGUIDEDISPLAY”, and the following US filings: U.S. Ser. No. 14/620,969“WAVEGUIDE GRATING DEVICE”; U.S. Ser. No. 15/468,536 “WAVEGUIDE GRATINGDEVICE”; U.S. Ser. No. 15/807,149 “WAVEGUIDE GRATING DEVICE”; and U.S.Ser. No. 16/178,104 “WAVEGUIDE GRATING DEVICE”, by Popovich et al.,which are incorporated herein in by reference in their entireties.Accordingly, all such modifications are intended to be included withinthe scope of the present disclosure. The order or sequence of anyprocess or method steps may be varied or re-sequenced according toalternative embodiments. Other substitutions, modifications, changes,and omissions may be made in the design, operating conditions andarrangement of the exemplary embodiments without departing from thescope of the present disclosure.

Doctrine of Equivalents

While the above description contains many specific embodiments of theinvention, these should not be construed as limitations on the scope ofthe invention, but rather as an example of one embodiment thereof. It istherefore to be understood that the present invention may be practicedin ways other than specifically described, without departing from thescope and spirit of the present invention. Thus, embodiments of thepresent invention should be considered in all respects as illustrativeand not restrictive. Accordingly, the scope of the invention should bedetermined not by the embodiments illustrated, but by the appendedclaims and their equivalents.

1. A waveguide display, comprising: a source of light; and a firstwaveguide comprising: a grating structure comprising first and secondgratings; and an input coupler configured to: couple a firstfield-of-view portion of light from said source of light into said firstwaveguide and towards said first grating; and couple a secondfield-of-view portion of light from said source of light into said firstwaveguide and towards said second grating; wherein: said first gratingis configured to: provide beam expansion in a first direction for saidfirst field-of-view portion of light; and provide beam expansion in saidfirst direction and beam extraction towards a viewer for said secondfield-of-view portion of light; said second grating is configured to:provide beam expansion in a second direction for said secondfield-of-view portion of light; and provide beam expansion in saidsecond direction and beam extraction towards a viewer for said firstfield-of-view portion of light; said input coupler, said first grating,and said second grating each comprises a grating vector; and saidgrating vectors of said input coupler, said first grating, and saidsecond grating provide a resultant vector with substantially zeromagnitude.
 2. The waveguide display of claim 1, wherein: said firstgrating comprises first and second grating prescriptions; and saidsecond grating comprises third and fourth grating prescriptions;wherein: said first grating prescription is configured to provide saidbeam expansion in said first direction for said first field-of-viewportion of light; said second grating prescription is configured toprovide beam expansion in said first direction and beam extractiontowards a viewer for said second field-of-view portion of light; saidthird grating prescription is configured to provide said beam expansionin said second direction for said second field-of-view portion of light;and said fourth grating prescription is configured to provide said beamexpansion in said second direction and beam extraction towards a viewerfor said first field-of-view portion of light.
 3. The waveguide displayof claim 2, wherein said first and second grating prescriptions are atleast partially multiplexed; and said third and fourth gratingprescriptions are at least partially multiplexed.
 4. The waveguidedisplay of claim 3, wherein said first grating at least partiallyoverlaps said second grating.
 5. The waveguide display of claim 4,wherein: said first waveguide comprises first and second grating layers;said first grating is disposed within said first grating layer; and saidsecond grating is disposed within said second grating layer.
 6. Thewaveguide display of claim 5, wherein said first waveguide furthercomprises a transparent layer disposed between and adjacent said firstand second grating layers.
 7. The waveguide display of claim 6, furthercomprising a second waveguide; wherein said first waveguide isconfigured to couple in a first spectral band of light; and said secondwaveguide is configured to couple in a second spectral band of light. 8.The waveguide display of claim 1, wherein said input coupler comprisesan input configuration selected from the group consisting of: an inputprism; an input grating; first and second input gratings; and an inputgrating comprising two multiplexed grating prescriptions.
 9. Thewaveguide display of claim 1, wherein said grating vector of said inputcoupler has a different magnitude than said grating vector of said firstgrating.
 10. The waveguide display of claim 1, wherein said source oflight provides at least two different wavelengths of light.
 11. A methodof displaying an image, the method comprising: providing a waveguidedisplay comprising a first waveguide supporting an input coupler and agrating structure comprising first and second gratings, wherein saidinput coupler, said first grating, and said second grating eachcomprises a grating vector, wherein said grating vectors of said inputcoupler, said first grating, and said second grating provide a resultantvector with substantially zero magnitude; coupling a first field of viewportion light into said waveguide via said input coupler; coupling asecond field-of-view portion light into said waveguide via said inputcoupler; expanding said first field-of-view portion light in a firstdirection using said first grating; expanding said first field-of-viewportion light in a second direction and extracting it from saidwaveguide using said second grating; expanding said second field-of-viewportion light in said second direction using said second grating; andexpanding said second field of view portion light in said firstdirection and extracting it from said waveguide using said firstgrating.
 12. The method of claim 11, wherein: said first gratingcomprises first and second grating prescriptions; and said secondgrating comprises third and fourth grating prescriptions; wherein: saidfirst field-of-view portion light is expanded in said first directionusing said first grating prescription; said second field-of-view portionlight is expanded in said first direction and extracted from saidwaveguide using said second grating prescription; said secondfield-of-view portion light is expanded in said second direction usingsaid third grating prescription; and said first field-of-view portionlight is expanded in said second direction and extracted from saidwaveguide using said fourth grating prescription.
 13. The method ofclaim 12, wherein said first and second grating prescriptions are atleast partially multiplexed; and said third and fourth gratingprescriptions are at least partially multiplexed.
 14. The method ofclaim 13, wherein said first grating at least partially overlaps saidsecond grating.
 15. The method of claim 14, wherein: said firstwaveguide comprises first and second grating layers; said first gratingis disposed within said first grating layer; and said second grating isdisposed within said second grating layer.
 16. The method of claim 15,wherein said first waveguide further comprises a transparent layerdisposed between and adjacent said first and second grating layers. 17.The method of claim 16, wherein said waveguide display further comprisesa second waveguide; wherein said first waveguide is configured to couplein a first spectral band of light; and said second waveguide isconfigured to couple in a second spectral band of light.
 18. The methodof claim 11, wherein said input coupler comprises an input configurationselected from the group consisting of: an input prism; an input grating;first and second input gratings; and an input grating comprising twomultiplexed grating prescriptions.
 19. The method of claim 11, whereinsaid grating vector of said input coupler has a different magnitude thansaid grating vector of said first grating.
 20. The method of claim 11,further comprising a source of light which provides at least twodifferent wavelengths of light.